JSON for Modern C++

Last update: Jan 4, 2023

Overview

Design goals
Sponsors
Integration
Examples
Supported compilers
License
Contact
Thanks
Used third-party tools
Projects using JSON for Modern C++
Notes
Execute unit tests

Design goals

There are myriads of JSON libraries out there, and each may even have its reason to exist. Our class had these design goals:

Intuitive syntax. In languages such as Python, JSON feels like a first class data type. We used all the operator magic of modern C++ to achieve the same feeling in your code. Check out the examples below and you'll know what I mean.
Trivial integration. Our whole code consists of a single header file json.hpp. That's it. No library, no subproject, no dependencies, no complex build system. The class is written in vanilla C++11. All in all, everything should require no adjustment of your compiler flags or project settings.
Serious testing. Our class is heavily unit-tested and covers 100% of the code, including all exceptional behavior. Furthermore, we checked with Valgrind and the Clang Sanitizers that there are no memory leaks. Google OSS-Fuzz additionally runs fuzz tests against all parsers 24/7, effectively executing billions of tests so far. To maintain high quality, the project is following the Core Infrastructure Initiative (CII) best practices.

Other aspects were not so important to us:

Memory efficiency. Each JSON object has an overhead of one pointer (the maximal size of a union) and one enumeration element (1 byte). The default generalization uses the following C++ data types: std::string for strings, int64_t, uint64_t or double for numbers, std::map for objects, std::vector for arrays, and bool for Booleans. However, you can template the generalized class basic_json to your needs.
Speed. There are certainly faster JSON libraries out there. However, if your goal is to speed up your development by adding JSON support with a single header, then this library is the way to go. If you know how to use a std::vector or std::map, you are already set.

See the contribution guidelines for more information.

Integration

json.hpp is the single required file in single_include/nlohmann or released here. You need to add

#include <nlohmann/json.hpp>

// for convenience
using json = nlohmann::json;

to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., -std=c++11 for GCC and Clang).

You can further use file include/nlohmann/json_fwd.hpp for forward-declarations. The installation of json_fwd.hpp (as part of cmake's install step), can be achieved by setting -DJSON_MultipleHeaders=ON.

CMake

You can also use the nlohmann_json::nlohmann_json interface target in CMake. This target populates the appropriate usage requirements for INTERFACE_INCLUDE_DIRECTORIES to point to the appropriate include directories and INTERFACE_COMPILE_FEATURES for the necessary C++11 flags.

External

To use this library from a CMake project, you can locate it directly with find_package() and use the namespaced imported target from the generated package configuration:

# CMakeLists.txt
find_package(nlohmann_json 3.2.0 REQUIRED)
...
add_library(foo ...)
...
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)

The package configuration file, nlohmann_jsonConfig.cmake, can be used either from an install tree or directly out of the build tree.

Embedded

To embed the library directly into an existing CMake project, place the entire source tree in a subdirectory and call add_subdirectory() in your CMakeLists.txt file:

# Typically you don't care so much for a third party library's tests to be
# run from your own project's code.
set(JSON_BuildTests OFF CACHE INTERNAL "")

# If you only include this third party in PRIVATE source files, you do not
# need to install it when your main project gets installed.
# set(JSON_Install OFF CACHE INTERNAL "")

# Don't use include(nlohmann_json/CMakeLists.txt) since that carries with it
# unintended consequences that will break the build.  It's generally
# discouraged (although not necessarily well documented as such) to use
# include(...) for pulling in other CMake projects anyways.
add_subdirectory(nlohmann_json)
...
add_library(foo ...)
...
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)

Embedded (FetchContent)

Since CMake v3.11, FetchContent can be used to automatically download the repository as a dependency at configure type.

Example:

include(FetchContent)

FetchContent_Declare(json
  GIT_REPOSITORY https://github.com/nlohmann/json.git
  GIT_TAG v3.7.3)

FetchContent_GetProperties(json)
if(NOT json_POPULATED)
  FetchContent_Populate(json)
  add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL)
endif()

target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)

Note: The repository https://github.com/nlohmann/json download size is huge. It contains all the dataset used for the benchmarks. You might want to depend on a smaller repository. For instance, you might want to replace the URL above by https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent

Supporting Both

To allow your project to support either an externally supplied or an embedded JSON library, you can use a pattern akin to the following:

# Top level CMakeLists.txt
project(FOO)
...
option(FOO_USE_EXTERNAL_JSON "Use an external JSON library" OFF)
...
add_subdirectory(thirdparty)
...
add_library(foo ...)
...
# Note that the namespaced target will always be available regardless of the
# import method
target_link_libraries(foo PRIVATE nlohmann_json::nlohmann_json)

# thirdparty/CMakeLists.txt
...
if(FOO_USE_EXTERNAL_JSON)
  find_package(nlohmann_json 3.2.0 REQUIRED)
else()
  set(JSON_BuildTests OFF CACHE INTERNAL "")
  add_subdirectory(nlohmann_json)
endif()
...

thirdparty/nlohmann_json is then a complete copy of this source tree.

Package Managers

🍺 If you are using OS X and Homebrew, just type brew tap nlohmann/json and brew install nlohmann-json and you're set. If you want the bleeding edge rather than the latest release, use brew install nlohmann-json --HEAD.

If you are using the Meson Build System, add this source tree as a meson subproject. You may also use the include.zip published in this project's Releases to reduce the size of the vendored source tree. Alternatively, you can get a wrap file by downloading it from Meson WrapDB, or simply use meson wrap install nlohmann_json. Please see the meson project for any issues regarding the packaging.

The provided meson.build can also be used as an alternative to cmake for installing nlohmann_json system-wide in which case a pkg-config file is installed. To use it, simply have your build system require the nlohmann_json pkg-config dependency. In Meson, it is preferred to use the dependency() object with a subproject fallback, rather than using the subproject directly.

If you are using Conan to manage your dependencies, merely add nlohmann_json/x.y.z to your conanfile's requires, where x.y.z is the release version you want to use. Please file issues here if you experience problems with the packages.

If you are using Spack to manage your dependencies, you can use the nlohmann-json package. Please see the spack project for any issues regarding the packaging.

If you are using hunter on your project for external dependencies, then you can use the nlohmann_json package. Please see the hunter project for any issues regarding the packaging.

If you are using Buckaroo, you can install this library's module with buckaroo add github.com/buckaroo-pm/nlohmann-json. Please file issues here. There is a demo repo here.

If you are using vcpkg on your project for external dependencies, then you can use the nlohmann-json package. Please see the vcpkg project for any issues regarding the packaging.

If you are using cget, you can install the latest development version with cget install nlohmann/json. A specific version can be installed with cget install nlohmann/[email protected]. Also, the multiple header version can be installed by adding the -DJSON_MultipleHeaders=ON flag (i.e., cget install nlohmann/json -DJSON_MultipleHeaders=ON).

If you are using CocoaPods, you can use the library by adding pod "nlohmann_json", '~>3.1.2' to your podfile (see an example). Please file issues here.

If you are using NuGet, you can use the package nlohmann.json. Please check this extensive description on how to use the package. Please files issues here.

If you are using conda, you can use the package nlohmann_json from conda-forge executing conda install -c conda-forge nlohmann_json. Please file issues here.

If you are using MSYS2, your can use the mingw-w64-nlohmann-json package, just type pacman -S mingw-w64-i686-nlohmann-json or pacman -S mingw-w64-x86_64-nlohmann-json for installation. Please file issues here if you experience problems with the packages.

If you are using build2, you can use the nlohmann-json package from the public repository https://cppget.org or directly from the package's sources repository. In your project's manifest file, just add depends: nlohmann-json (probably with some version constraints). If you are not familiar with using dependencies in build2, please read this introduction. Please file issues here if you experience problems with the packages.

If you are using wsjcpp, you can use the command wsjcpp install "https://github.com/nlohmann/json:develop" to get the latest version. Note you can change the branch ":develop" to an existing tag or another branch.

If you are using CPM.cmake, you can check this example. After adding CPM script to your project, implement the following snippet to your CMake:

CPMAddPackage(
    NAME nlohmann_json
    GITHUB_REPOSITORY nlohmann/json
    VERSION 3.9.1)

Pkg-config

If you are using bare Makefiles, you can use pkg-config to generate the include flags that point to where the library is installed:

pkg-config nlohmann_json --cflags

Users of the Meson build system will also be able to use a system wide library, which will be found by pkg-config:

json = dependency('nlohmann_json', required: true)

Examples

Beside the examples below, you may want to check the documentation where each function contains a separate code example (e.g., check out emplace()). All example files can be compiled and executed on their own (e.g., file emplace.cpp).

JSON as first-class data type

Here are some examples to give you an idea how to use the class.

Assume you want to create the JSON object

{
  "pi": 3.141,
  "happy": true,
  "name": "Niels",
  "nothing": null,
  "answer": {
    "everything": 42
  },
  "list": [1, 0, 2],
  "object": {
    "currency": "USD",
    "value": 42.99
  }
}

With this library, you could write:

// create an empty structure (null)
json j;

// add a number that is stored as double (note the implicit conversion of j to an object)
j["pi"] = 3.141;

// add a Boolean that is stored as bool
j["happy"] = true;

// add a string that is stored as std::string
j["name"] = "Niels";

// add another null object by passing nullptr
j["nothing"] = nullptr;

// add an object inside the object
j["answer"]["everything"] = 42;

// add an array that is stored as std::vector (using an initializer list)
j["list"] = { 1, 0, 2 };

// add another object (using an initializer list of pairs)
j["object"] = { {"currency", "USD"}, {"value", 42.99} };

// instead, you could also write (which looks very similar to the JSON above)
json j2 = {
  {"pi", 3.141},
  {"happy", true},
  {"name", "Niels"},
  {"nothing", nullptr},
  {"answer", {
    {"everything", 42}
  }},
  {"list", {1, 0, 2}},
  {"object", {
    {"currency", "USD"},
    {"value", 42.99}
  }}
};

Note that in all these cases, you never need to "tell" the compiler which JSON value type you want to use. If you want to be explicit or express some edge cases, the functions json::array() and json::object() will help:

// a way to express the empty array []
json empty_array_explicit = json::array();

// ways to express the empty object {}
json empty_object_implicit = json({});
json empty_object_explicit = json::object();

// a way to express an _array_ of key/value pairs [["currency", "USD"], ["value", 42.99]]
json array_not_object = json::array({ {"currency", "USD"}, {"value", 42.99} });

Serialization / Deserialization

To/from strings

You can create a JSON value (deserialization) by appending _json to a string literal:

// create object from string literal
json j = "{ \"happy\": true, \"pi\": 3.141 }"_json;

// or even nicer with a raw string literal
auto j2 = R"(
  {
    "happy": true,
    "pi": 3.141
  }
)"_json;

Note that without appending the _json suffix, the passed string literal is not parsed, but just used as JSON string value. That is, json j = "{ \"happy\": true, \"pi\": 3.141 }" would just store the string "{ "happy": true, "pi": 3.141 }" rather than parsing the actual object.

The above example can also be expressed explicitly using json::parse():

// parse explicitly
auto j3 = json::parse("{ \"happy\": true, \"pi\": 3.141 }");

You can also get a string representation of a JSON value (serialize):

// explicit conversion to string
std::string s = j.dump();    // {"happy":true,"pi":3.141}

// serialization with pretty printing
// pass in the amount of spaces to indent
std::cout << j.dump(4) << std::endl;
// {
//     "happy": true,
//     "pi": 3.141
// }

Note the difference between serialization and assignment:

// store a string in a JSON value
json j_string = "this is a string";

// retrieve the string value
auto cpp_string = j_string.get<std::string>();
// retrieve the string value (alternative when an variable already exists)
std::string cpp_string2;
j_string.get_to(cpp_string2);

// retrieve the serialized value (explicit JSON serialization)
std::string serialized_string = j_string.dump();

// output of original string
std::cout << cpp_string << " == " << cpp_string2 << " == " << j_string.get<std::string>() << '\n';
// output of serialized value
std::cout << j_string << " == " << serialized_string << std::endl;

.dump() returns the originally stored string value.

Note the library only supports UTF-8. When you store strings with different encodings in the library, calling dump() may throw an exception unless json::error_handler_t::replace or json::error_handler_t::ignore are used as error handlers.

To/from streams (e.g. files, string streams)

You can also use streams to serialize and deserialize:

// deserialize from standard input
json j;
std::cin >> j;

// serialize to standard output
std::cout << j;

// the setw manipulator was overloaded to set the indentation for pretty printing
std::cout << std::setw(4) << j << std::endl;

These operators work for any subclasses of std::istream or std::ostream. Here is the same example with files:

// read a JSON file
std::ifstream i("file.json");
json j;
i >> j;

// write prettified JSON to another file
std::ofstream o("pretty.json");
o << std::setw(4) << j << std::endl;

Please note that setting the exception bit for failbit is inappropriate for this use case. It will result in program termination due to the noexcept specifier in use.

Read from iterator range

You can also parse JSON from an iterator range; that is, from any container accessible by iterators whose value_type is an integral type of 1, 2 or 4 bytes, which will be interpreted as UTF-8, UTF-16 and UTF-32 respectively. For instance, a std::vector<std::uint8_t>, or a std::list<std::uint16_t>:

std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'};
json j = json::parse(v.begin(), v.end());

You may leave the iterators for the range [begin, end):

std::vector<std::uint8_t> v = {'t', 'r', 'u', 'e'};
json j = json::parse(v);

Custom data source

Since the parse function accepts arbitrary iterator ranges, you can provide your own data sources by implementing the LegacyInputIterator concept.

struct MyContainer {
  void advance();
  const char& get_current();
};

struct MyIterator {
    using difference_type = std::ptrdiff_t;
    using value_type = char;
    using pointer = const char*;
    using reference = const char&;
    using iterator_category = std::input_iterator_tag;

    MyIterator& operator++() {
        MyContainer.advance();
        return *this;
    }

    bool operator!=(const MyIterator& rhs) const {
        return rhs.target != target;
    }

    reference operator*() const {
        return target.get_current();
    }

    MyContainer* target = nullptr;
};

MyIterator begin(MyContainer& tgt) {
    return MyIterator{&tgt};
}

MyIterator end(const MyContainer&) {
    return {};
}

void foo() {
    MyContainer c;
    json j = json::parse(c);
}

SAX interface

The library uses a SAX-like interface with the following functions:

// called when null is parsed
bool null();

// called when a boolean is parsed; value is passed
bool boolean(bool val);

// called when a signed or unsigned integer number is parsed; value is passed
bool number_integer(number_integer_t val);
bool number_unsigned(number_unsigned_t val);

// called when a floating-point number is parsed; value and original string is passed
bool number_float(number_float_t val, const string_t& s);

// called when a string is parsed; value is passed and can be safely moved away
bool string(string_t& val);
// called when a binary value is parsed; value is passed and can be safely moved away
bool binary(binary_t& val);

// called when an object or array begins or ends, resp. The number of elements is passed (or -1 if not known)
bool start_object(std::size_t elements);
bool end_object();
bool start_array(std::size_t elements);
bool end_array();
// called when an object key is parsed; value is passed and can be safely moved away
bool key(string_t& val);

// called when a parse error occurs; byte position, the last token, and an exception is passed
bool parse_error(std::size_t position, const std::string& last_token, const detail::exception& ex);

The return value of each function determines whether parsing should proceed.

To implement your own SAX handler, proceed as follows:

Implement the SAX interface in a class. You can use class nlohmann::json_sax<json> as base class, but you can also use any class where the functions described above are implemented and public.
Create an object of your SAX interface class, e.g. my_sax.
Call bool json::sax_parse(input, &my_sax); where the first parameter can be any input like a string or an input stream and the second parameter is a pointer to your SAX interface.

Note the sax_parse function only returns a bool indicating the result of the last executed SAX event. It does not return a json value - it is up to you to decide what to do with the SAX events. Furthermore, no exceptions are thrown in case of a parse error - it is up to you what to do with the exception object passed to your parse_error implementation. Internally, the SAX interface is used for the DOM parser (class json_sax_dom_parser) as well as the acceptor (json_sax_acceptor), see file json_sax.hpp.

STL-like access

We designed the JSON class to behave just like an STL container. In fact, it satisfies the ReversibleContainer requirement.

// create an array using push_back
json j;
j.push_back("foo");
j.push_back(1);
j.push_back(true);

// also use emplace_back
j.emplace_back(1.78);

// iterate the array
for (json::iterator it = j.begin(); it != j.end(); ++it) {
  std::cout << *it << '\n';
}

// range-based for
for (auto& element : j) {
  std::cout << element << '\n';
}

// getter/setter
const auto tmp = j[0].get<std::string>();
j[1] = 42;
bool foo = j.at(2);

// comparison
j == "[\"foo\", 42, true, 1.78]"_json;  // true

// other stuff
j.size();     // 3 entries
j.empty();    // false
j.type();     // json::value_t::array
j.clear();    // the array is empty again

// convenience type checkers
j.is_null();
j.is_boolean();
j.is_number();
j.is_object();
j.is_array();
j.is_string();

// create an object
json o;
o["foo"] = 23;
o["bar"] = false;
o["baz"] = 3.141;

// also use emplace
o.emplace("weather", "sunny");

// special iterator member functions for objects
for (json::iterator it = o.begin(); it != o.end(); ++it) {
  std::cout << it.key() << " : " << it.value() << "\n";
}

// the same code as range for
for (auto& el : o.items()) {
  std::cout << el.key() << " : " << el.value() << "\n";
}

// even easier with structured bindings (C++17)
for (auto& [key, value] : o.items()) {
  std::cout << key << " : " << value << "\n";
}

// find an entry
if (o.contains("foo")) {
  // there is an entry with key "foo"
}

// or via find and an iterator
if (o.find("foo") != o.end()) {
  // there is an entry with key "foo"
}

// or simpler using count()
int foo_present = o.count("foo"); // 1
int fob_present = o.count("fob"); // 0

// delete an entry
o.erase("foo");

Conversion from STL containers

Any sequence container (std::array, std::vector, std::deque, std::forward_list, std::list) whose values can be used to construct JSON values (e.g., integers, floating point numbers, Booleans, string types, or again STL containers described in this section) can be used to create a JSON array. The same holds for similar associative containers (std::set, std::multiset, std::unordered_set, std::unordered_multiset), but in these cases the order of the elements of the array depends on how the elements are ordered in the respective STL container.

std::vector<int> c_vector {1, 2, 3, 4};
json j_vec(c_vector);
// [1, 2, 3, 4]

std::deque<double> c_deque {1.2, 2.3, 3.4, 5.6};
json j_deque(c_deque);
// [1.2, 2.3, 3.4, 5.6]

std::list<bool> c_list {true, true, false, true};
json j_list(c_list);
// [true, true, false, true]

std::forward_list<int64_t> c_flist {12345678909876, 23456789098765, 34567890987654, 45678909876543};
json j_flist(c_flist);
// [12345678909876, 23456789098765, 34567890987654, 45678909876543]

std::array<unsigned long, 4> c_array {{1, 2, 3, 4}};
json j_array(c_array);
// [1, 2, 3, 4]

std::set<std::string> c_set {"one", "two", "three", "four", "one"};
json j_set(c_set); // only one entry for "one" is used
// ["four", "one", "three", "two"]

std::unordered_set<std::string> c_uset {"one", "two", "three", "four", "one"};
json j_uset(c_uset); // only one entry for "one" is used
// maybe ["two", "three", "four", "one"]

std::multiset<std::string> c_mset {"one", "two", "one", "four"};
json j_mset(c_mset); // both entries for "one" are used
// maybe ["one", "two", "one", "four"]

std::unordered_multiset<std::string> c_umset {"one", "two", "one", "four"};
json j_umset(c_umset); // both entries for "one" are used
// maybe ["one", "two", "one", "four"]

Likewise, any associative key-value containers (std::map, std::multimap, std::unordered_map, std::unordered_multimap) whose keys can construct an std::string and whose values can be used to construct JSON values (see examples above) can be used to create a JSON object. Note that in case of multimaps only one key is used in the JSON object and the value depends on the internal order of the STL container.

std::map<std::string, int> c_map { {"one", 1}, {"two", 2}, {"three", 3} };
json j_map(c_map);
// {"one": 1, "three": 3, "two": 2 }

std::unordered_map<const char*, double> c_umap { {"one", 1.2}, {"two", 2.3}, {"three", 3.4} };
json j_umap(c_umap);
// {"one": 1.2, "two": 2.3, "three": 3.4}

std::multimap<std::string, bool> c_mmap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
json j_mmap(c_mmap); // only one entry for key "three" is used
// maybe {"one": true, "two": true, "three": true}

std::unordered_multimap<std::string, bool> c_ummap { {"one", true}, {"two", true}, {"three", false}, {"three", true} };
json j_ummap(c_ummap); // only one entry for key "three" is used
// maybe {"one": true, "two": true, "three": true}

JSON Pointer and JSON Patch

The library supports JSON Pointer (RFC 6901) as alternative means to address structured values. On top of this, JSON Patch (RFC 6902) allows to describe differences between two JSON values - effectively allowing patch and diff operations known from Unix.

// a JSON value
json j_original = R"({
  "baz": ["one", "two", "three"],
  "foo": "bar"
})"_json;

// access members with a JSON pointer (RFC 6901)
j_original["/baz/1"_json_pointer];
// "two"

// a JSON patch (RFC 6902)
json j_patch = R"([
  { "op": "replace", "path": "/baz", "value": "boo" },
  { "op": "add", "path": "/hello", "value": ["world"] },
  { "op": "remove", "path": "/foo"}
])"_json;

// apply the patch
json j_result = j_original.patch(j_patch);
// {
//    "baz": "boo",
//    "hello": ["world"]
// }

// calculate a JSON patch from two JSON values
json::diff(j_result, j_original);
// [
//   { "op":" replace", "path": "/baz", "value": ["one", "two", "three"] },
//   { "op": "remove","path": "/hello" },
//   { "op": "add", "path": "/foo", "value": "bar" }
// ]

JSON Merge Patch

The library supports JSON Merge Patch (RFC 7386) as a patch format. Instead of using JSON Pointer (see above) to specify values to be manipulated, it describes the changes using a syntax that closely mimics the document being modified.

// a JSON value
json j_document = R"({
  "a": "b",
  "c": {
    "d": "e",
    "f": "g"
  }
})"_json;

// a patch
json j_patch = R"({
  "a":"z",
  "c": {
    "f": null
  }
})"_json;

// apply the patch
j_document.merge_patch(j_patch);
// {
//  "a": "z",
//  "c": {
//    "d": "e"
//  }
// }

Implicit conversions

Supported types can be implicitly converted to JSON values.

It is recommended to NOT USE implicit conversions FROM a JSON value. You can find more details about this recommendation here. You can switch off implicit conversions by defining JSON_USE_IMPLICIT_CONVERSIONS to 0 before including the json.hpp header. When using CMake, you can also achieve this by setting the option JSON_ImplicitConversions to OFF.

// strings
std::string s1 = "Hello, world!";
json js = s1;
auto s2 = js.get<std::string>();
// NOT RECOMMENDED
std::string s3 = js;
std::string s4;
s4 = js;

// Booleans
bool b1 = true;
json jb = b1;
auto b2 = jb.get<bool>();
// NOT RECOMMENDED
bool b3 = jb;
bool b4;
b4 = jb;

// numbers
int i = 42;
json jn = i;
auto f = jn.get<double>();
// NOT RECOMMENDED
double f2 = jb;
double f3;
f3 = jb;

// etc.

Note that char types are not automatically converted to JSON strings, but to integer numbers. A conversion to a string must be specified explicitly:

char ch = 'A';                       // ASCII value 65
json j_default = ch;                 // stores integer number 65
json j_string = std::string(1, ch);  // stores string "A"

Arbitrary types conversions

Every type can be serialized in JSON, not just STL containers and scalar types. Usually, you would do something along those lines:

namespace ns {
    // a simple struct to model a person
    struct person {
        std::string name;
        std::string address;
        int age;
    };
}

ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};

// convert to JSON: copy each value into the JSON object
json j;
j["name"] = p.name;
j["address"] = p.address;
j["age"] = p.age;

// ...

// convert from JSON: copy each value from the JSON object
ns::person p {
    j["name"].get<std::string>(),
    j["address"].get<std::string>(),
    j["age"].get<int>()
};

It works, but that's quite a lot of boilerplate... Fortunately, there's a better way:

// create a person
ns::person p {"Ned Flanders", "744 Evergreen Terrace", 60};

// conversion: person -> json
json j = p;

std::cout << j << std::endl;
// {"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}

// conversion: json -> person
auto p2 = j.get<ns::person>();

// that's it
assert(p == p2);

Basic usage

To make this work with one of your types, you only need to provide two functions:

using nlohmann::json;

namespace ns {
    void to_json(json& j, const person& p) {
        j = json{{"name", p.name}, {"address", p.address}, {"age", p.age}};
    }

    void from_json(const json& j, person& p) {
        j.at("name").get_to(p.name);
        j.at("address").get_to(p.address);
        j.at("age").get_to(p.age);
    }
} // namespace ns

That's all! When calling the json constructor with your type, your custom to_json method will be automatically called. Likewise, when calling get<your_type>() or get_to(your_type&), the from_json method will be called.

Some important things:

Those methods MUST be in your type's namespace (which can be the global namespace), or the library will not be able to locate them (in this example, they are in namespace ns, where person is defined).
Those methods MUST be available (e.g., proper headers must be included) everywhere you use these conversions. Look at issue 1108 for errors that may occur otherwise.
When using get<your_type>(), your_type MUST be DefaultConstructible. (There is a way to bypass this requirement described later.)
In function from_json, use function at() to access the object values rather than operator[]. In case a key does not exist, at throws an exception that you can handle, whereas operator[] exhibits undefined behavior.
You do not need to add serializers or deserializers for STL types like std::vector: the library already implements these.

Simplify your life with macros

If you just want to serialize/deserialize some structs, the to_json/from_json functions can be a lot of boilerplate.

There are two macros to make your life easier as long as you (1) want to use a JSON object as serialization and (2) want to use the member variable names as object keys in that object:

NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(name, member1, member2, ...) is to be defined inside of the namespace of the class/struct to create code for.
NLOHMANN_DEFINE_TYPE_INTRUSIVE(name, member1, member2, ...) is to be defined inside of the class/struct to create code for. This macro can also access private members.

In both macros, the first parameter is the name of the class/struct, and all remaining parameters name the members.

Examples

The to_json/from_json functions for the person struct above can be created with:

namespace ns {
    NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, address, age)
}

Here is an example with private members, where NLOHMANN_DEFINE_TYPE_INTRUSIVE is needed:

namespace ns {
    class address {
      private:
        std::string street;
        int housenumber;
        int postcode;

      public:
        NLOHMANN_DEFINE_TYPE_INTRUSIVE(address, street, housenumber, postcode)
    };
}

How do I convert third-party types?

This requires a bit more advanced technique. But first, let's see how this conversion mechanism works:

The library uses JSON Serializers to convert types to json. The default serializer for nlohmann::json is nlohmann::adl_serializer (ADL means Argument-Dependent Lookup).

It is implemented like this (simplified):

template <typename T>
struct adl_serializer {
    static void to_json(json& j, const T& value) {
        // calls the "to_json" method in T's namespace
    }

    static void from_json(const json& j, T& value) {
        // same thing, but with the "from_json" method
    }
};

This serializer works fine when you have control over the type's namespace. However, what about boost::optional or std::filesystem::path (C++17)? Hijacking the boost namespace is pretty bad, and it's illegal to add something other than template specializations to std...

To solve this, you need to add a specialization of adl_serializer to the nlohmann namespace, here's an example:

// partial specialization (full specialization works too)
namespace nlohmann {
    template <typename T>
    struct adl_serializer<boost::optional<T>> {
        static void to_json(json& j, const boost::optional<T>& opt) {
            if (opt == boost::none) {
                j = nullptr;
            } else {
              j = *opt; // this will call adl_serializer<T>::to_json which will
                        // find the free function to_json in T's namespace!
            }
        }

        static void from_json(const json& j, boost::optional<T>& opt) {
            if (j.is_null()) {
                opt = boost::none;
            } else {
                opt = j.get<T>(); // same as above, but with
                                  // adl_serializer<T>::from_json
            }
        }
    };
}

How can I use `get()` for non-default constructible/non-copyable types?

There is a way, if your type is MoveConstructible. You will need to specialize the adl_serializer as well, but with a special from_json overload:

struct move_only_type {
    move_only_type() = delete;
    move_only_type(int ii): i(ii) {}
    move_only_type(const move_only_type&) = delete;
    move_only_type(move_only_type&&) = default;

    int i;
};

namespace nlohmann {
    template <>
    struct adl_serializer<move_only_type> {
        // note: the return type is no longer 'void', and the method only takes
        // one argument
        static move_only_type from_json(const json& j) {
            return {j.get<int>()};
        }

        // Here's the catch! You must provide a to_json method! Otherwise you
        // will not be able to convert move_only_type to json, since you fully
        // specialized adl_serializer on that type
        static void to_json(json& j, move_only_type t) {
            j = t.i;
        }
    };
}

Can I write my own serializer? (Advanced use)

Yes. You might want to take a look at unit-udt.cpp in the test suite, to see a few examples.

If you write your own serializer, you'll need to do a few things:

use a different basic_json alias than nlohmann::json (the last template parameter of basic_json is the JSONSerializer)
use your basic_json alias (or a template parameter) in all your to_json/from_json methods
use nlohmann::to_json and nlohmann::from_json when you need ADL

Here is an example, without simplifications, that only accepts types with a size <= 32, and uses ADL.

// You should use void as a second template argument
// if you don't need compile-time checks on T
template<typename T, typename SFINAE = typename std::enable_if<sizeof(T) <= 32>::type>
struct less_than_32_serializer {
    template <typename BasicJsonType>
    static void to_json(BasicJsonType& j, T value) {
        // we want to use ADL, and call the correct to_json overload
        using nlohmann::to_json; // this method is called by adl_serializer,
                                 // this is where the magic happens
        to_json(j, value);
    }

    template <typename BasicJsonType>
    static void from_json(const BasicJsonType& j, T& value) {
        // same thing here
        using nlohmann::from_json;
        from_json(j, value);
    }
};

Be very careful when reimplementing your serializer, you can stack overflow if you don't pay attention:

template <typename T, void>
struct bad_serializer
{
    template <typename BasicJsonType>
    static void to_json(BasicJsonType& j, const T& value) {
      // this calls BasicJsonType::json_serializer<T>::to_json(j, value);
      // if BasicJsonType::json_serializer == bad_serializer ... oops!
      j = value;
    }

    template <typename BasicJsonType>
    static void to_json(const BasicJsonType& j, T& value) {
      // this calls BasicJsonType::json_serializer<T>::from_json(j, value);
      // if BasicJsonType::json_serializer == bad_serializer ... oops!
      value = j.template get<T>(); // oops!
    }
};

Specializing enum conversion

By default, enum values are serialized to JSON as integers. In some cases this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later de-serialized JSON data may be undefined or a different enum value than was originally intended.

It is possible to more precisely specify how a given enum is mapped to and from JSON as shown below:

// example enum type declaration
enum TaskState {
    TS_STOPPED,
    TS_RUNNING,
    TS_COMPLETED,
    TS_INVALID=-1,
};

// map TaskState values to JSON as strings
NLOHMANN_JSON_SERIALIZE_ENUM( TaskState, {
    {TS_INVALID, nullptr},
    {TS_STOPPED, "stopped"},
    {TS_RUNNING, "running"},
    {TS_COMPLETED, "completed"},
})

The NLOHMANN_JSON_SERIALIZE_ENUM() macro declares a set of to_json() / from_json() functions for type TaskState while avoiding repetition and boilerplate serialization code.

Usage:

// enum to JSON as string
json j = TS_STOPPED;
assert(j == "stopped");

// json string to enum
json j3 = "running";
assert(j3.get<TaskState>() == TS_RUNNING);

// undefined json value to enum (where the first map entry above is the default)
json jPi = 3.14;
assert(jPi.get<TaskState>() == TS_INVALID );

Just as in Arbitrary Type Conversions above,

NLOHMANN_JSON_SERIALIZE_ENUM() MUST be declared in your enum type's namespace (which can be the global namespace), or the library will not be able to locate it and it will default to integer serialization.
It MUST be available (e.g., proper headers must be included) everywhere you use the conversions.

Other Important points:

When using get<ENUM_TYPE>(), undefined JSON values will default to the first pair specified in your map. Select this default pair carefully.
If an enum or JSON value is specified more than once in your map, the first matching occurrence from the top of the map will be returned when converting to or from JSON.

Binary formats (BSON, CBOR, MessagePack, and UBJSON)

Though JSON is a ubiquitous data format, it is not a very compact format suitable for data exchange, for instance over a network. Hence, the library supports BSON (Binary JSON), CBOR (Concise Binary Object Representation), MessagePack, and UBJSON (Universal Binary JSON Specification) to efficiently encode JSON values to byte vectors and to decode such vectors.

// create a JSON value
json j = R"({"compact": true, "schema": 0})"_json;

// serialize to BSON
std::vector<std::uint8_t> v_bson = json::to_bson(j);

// 0x1B, 0x00, 0x00, 0x00, 0x08, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x00, 0x01, 0x10, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00

// roundtrip
json j_from_bson = json::from_bson(v_bson);

// serialize to CBOR
std::vector<std::uint8_t> v_cbor = json::to_cbor(j);

// 0xA2, 0x67, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xF5, 0x66, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00

// roundtrip
json j_from_cbor = json::from_cbor(v_cbor);

// serialize to MessagePack
std::vector<std::uint8_t> v_msgpack = json::to_msgpack(j);

// 0x82, 0xA7, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0xC3, 0xA6, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x00

// roundtrip
json j_from_msgpack = json::from_msgpack(v_msgpack);

// serialize to UBJSON
std::vector<std::uint8_t> v_ubjson = json::to_ubjson(j);

// 0x7B, 0x69, 0x07, 0x63, 0x6F, 0x6D, 0x70, 0x61, 0x63, 0x74, 0x54, 0x69, 0x06, 0x73, 0x63, 0x68, 0x65, 0x6D, 0x61, 0x69, 0x00, 0x7D

// roundtrip
json j_from_ubjson = json::from_ubjson(v_ubjson);

The library also supports binary types from BSON, CBOR (byte strings), and MessagePack (bin, ext, fixext). They are stored by default as std::vector<std::uint8_t> to be processed outside of the library.

// CBOR byte string with payload 0xCAFE
std::vector<std::uint8_t> v = {0x42, 0xCA, 0xFE};

// read value
json j = json::from_cbor(v);

// the JSON value has type binary
j.is_binary(); // true

// get reference to stored binary value
auto& binary = j.get_binary();

// the binary value has no subtype (CBOR has no binary subtypes)
binary.has_subtype(); // false

// access std::vector<std::uint8_t> member functions
binary.size(); // 2
binary[0]; // 0xCA
binary[1]; // 0xFE

// set subtype to 0x10
binary.set_subtype(0x10);

// serialize to MessagePack
auto cbor = json::to_msgpack(j); // 0xD5 (fixext2), 0x10, 0xCA, 0xFE

Supported compilers

Though it's 2021 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:

GCC 4.8 - 11.0 (and possibly later)
Clang 3.4 - 11.0 (and possibly later)
Apple Clang 9.1 - 12.3 (and possibly later)
Intel C++ Compiler 17.0.2 (and possibly later)
Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
Microsoft Visual C++ 2017 / Build Tools 15.5.180.51428 (and possibly later)
Microsoft Visual C++ 2019 / Build Tools 16.3.1+1def00d3d (and possibly later)

I would be happy to learn about other compilers/versions.

Please note:

GCC 4.8 has a bug 57824): multiline raw strings cannot be the arguments to macros. Don't use multiline raw strings directly in macros with this compiler.
Android defaults to using very old compilers and C++ libraries. To fix this, add the following to your Application.mk. This will switch to the LLVM C++ library, the Clang compiler, and enable C++11 and other features disabled by default.
```
APP_STL := c++_shared
NDK_TOOLCHAIN_VERSION := clang3.6
APP_CPPFLAGS += -frtti -fexceptions
```
The code compiles successfully with Android NDK, Revision 9 - 11 (and possibly later) and CrystaX's Android NDK version 10.
For GCC running on MinGW or Android SDK, the error 'to_string' is not a member of 'std' (or similarly, for strtod or strtof) may occur. Note this is not an issue with the code, but rather with the compiler itself. On Android, see above to build with a newer environment. For MinGW, please refer to this site and this discussion for information on how to fix this bug. For Android NDK using APP_STL := gnustl_static, please refer to this discussion.
Unsupported versions of GCC and Clang are rejected by #error directives. This can be switched off by defining JSON_SKIP_UNSUPPORTED_COMPILER_CHECK. Note that you can expect no support in this case.

The following compilers are currently used in continuous integration at Travis, AppVeyor, GitHub Actions, and CircleCI:

Compiler	Operating System	CI Provider
Apple Clang 10.0.1 (clang-1001.0.46.4); Xcode 10.2.1	macOS 10.14.4	Travis
Apple Clang 11.0.0 (clang-1100.0.33.12); Xcode 11.2.1	macOS 10.14.6	Travis
Apple Clang 11.0.3 (clang-1103.0.32.59); Xcode 11.4.1	macOS 10.15.4	GitHub Actions
Apple Clang 12.0.0 (clang-1200.0.22.7); Xcode 11.4.1	macOS 10.15.5	Travis
Clang 3.5.0 (3.5.0-4ubuntu2~trusty2)	Ubuntu 14.04.5 LTS	Travis
Clang 3.6.2 (3.6.2-svn240577-1~exp1)	Ubuntu 14.04.5 LTS	Travis
Clang 3.7.1 (3.7.1-svn253571-1~exp1)	Ubuntu 14.04.5 LTS	Travis
Clang 3.8.0 (3.8.0-2ubuntu3~trusty5)	Ubuntu 14.04.5 LTS	Travis
Clang 3.9.1 (3.9.1-4ubuntu3~14.04.3)	Ubuntu 14.04.5 LTS	Travis
Clang 4.0.1 (4.0.1-svn305264-1~exp1)	Ubuntu 14.04.5 LTS	Travis
Clang 5.0.2 (version 5.0.2-svn328729-1~exp1~20180509123505.100)	Ubuntu 14.04.5 LTS	Travis
Clang 6.0.1 (6.0.1-svn334776-1~exp1~20190309042707.121)	Ubuntu 14.04.5 LTS	Travis
Clang 7.1.0 (7.1.0-svn353565-1~exp1~20190419134007.64)	Ubuntu 14.04.5 LTS	Travis
Clang 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)	Ubuntu 18.04.4 LTS	Travis
Clang 9.0.0 (x86_64-pc-windows-msvc)	Windows-10.0.17763	GitHub Actions
Clang 10.0.0 (x86_64-pc-windows-msvc)	Windows-10.0.17763	GitHub Actions
GCC 4.8.5 (Ubuntu 4.8.5-4ubuntu8~14.04.2)	Ubuntu 14.04.5 LTS	Travis
GCC 4.9.4 (Ubuntu 4.9.4-2ubuntu1~14.04.1)	Ubuntu 14.04.5 LTS	Travis
GCC 5.5.0 (Ubuntu 5.5.0-12ubuntu1~14.04)	Ubuntu 14.04.5 LTS	Travis
GCC 6.3.0 (Debian 6.3.0-18+deb9u1)	Debian 9	Circle CI
GCC 6.5.0 (Ubuntu 6.5.0-2ubuntu1~14.04.1)	Ubuntu 14.04.5 LTS	Travis
GCC 7.3.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project)	Windows-6.3.9600	AppVeyor
GCC 7.5.0 (Ubuntu 7.5.0-3ubuntu1~14.04.1)	Ubuntu 14.04.5 LTS	Travis
GCC 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)	Ubuntu 18.04.4 LTS	GitHub Actions
GCC 8.4.0 (Ubuntu 8.4.0-1ubuntu1~14.04)	Ubuntu 14.04.5 LTS	Travis
GCC 9.3.0 (Ubuntu 9.3.0-11ubuntu0~14.04)	Ubuntu 14.04.5 LTS	Travis
GCC 10.1.0 (Arch Linux latest)	Arch Linux	Circle CI
MSVC 19.0.24241.7 (Build Engine version 14.0.25420.1)	Windows-6.3.9600	AppVeyor
MSVC 19.16.27035.0 (15.9.21+g9802d43bc3 for .NET Framework)	Windows-10.0.14393	AppVeyor
MSVC 19.25.28614.0 (Build Engine version 16.5.0+d4cbfca49 for .NET Framework)	Windows-10.0.17763	AppVeyor
MSVC 19.25.28614.0 (Build Engine version 16.5.0+d4cbfca49 for .NET Framework)	Windows-10.0.17763	GitHub Actions
MSVC 19.25.28614.0 (Build Engine version 16.5.0+d4cbfca49 for .NET Framework) with ClangCL 10.0.0	Windows-10.0.17763	GitHub Actions

License

The class is licensed under the MIT License:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

The class contains a copy of Hedley from Evan Nemerson which is licensed as CC0-1.0.

Contact

If you have questions regarding the library, I would like to invite you to open an issue at GitHub. Please describe your request, problem, or question as detailed as possible, and also mention the version of the library you are using as well as the version of your compiler and operating system. Opening an issue at GitHub allows other users and contributors to this library to collaborate. For instance, I have little experience with MSVC, and most issues in this regard have been solved by a growing community. If you have a look at the closed issues, you will see that we react quite timely in most cases.

Only if your request would contain confidential information, please send me an email. For encrypted messages, please use this key.

Security

Commits by Niels Lohmann and releases are signed with this PGP Key.

Thanks

I deeply appreciate the help of the following people.

Teemperor implemented CMake support and lcov integration, realized escape and Unicode handling in the string parser, and fixed the JSON serialization.
elliotgoodrich fixed an issue with double deletion in the iterator classes.
kirkshoop made the iterators of the class composable to other libraries.
wancw fixed a bug that hindered the class to compile with Clang.
Tomas Åblad found a bug in the iterator implementation.
Joshua C. Randall fixed a bug in the floating-point serialization.
Aaron Burghardt implemented code to parse streams incrementally. Furthermore, he greatly improved the parser class by allowing the definition of a filter function to discard undesired elements while parsing.
Daniel Kopeček fixed a bug in the compilation with GCC 5.0.
Florian Weber fixed a bug in and improved the performance of the comparison operators.
Eric Cornelius pointed out a bug in the handling with NaN and infinity values. He also improved the performance of the string escaping.
易思龙 implemented a conversion from anonymous enums.
kepkin patiently pushed forward the support for Microsoft Visual studio.
gregmarr simplified the implementation of reverse iterators and helped with numerous hints and improvements. In particular, he pushed forward the implementation of user-defined types.
Caio Luppi fixed a bug in the Unicode handling.
dariomt fixed some typos in the examples.
Daniel Frey cleaned up some pointers and implemented exception-safe memory allocation.
Colin Hirsch took care of a small namespace issue.
Huu Nguyen correct a variable name in the documentation.
Silverweed overloaded parse() to accept an rvalue reference.
dariomt fixed a subtlety in MSVC type support and implemented the get_ref() function to get a reference to stored values.
ZahlGraf added a workaround that allows compilation using Android NDK.
whackashoe replaced a function that was marked as unsafe by Visual Studio.
406345 fixed two small warnings.
Glen Fernandes noted a potential portability problem in the has_mapped_type function.
Corbin Hughes fixed some typos in the contribution guidelines.
twelsby fixed the array subscript operator, an issue that failed the MSVC build, and floating-point parsing/dumping. He further added support for unsigned integer numbers and implemented better roundtrip support for parsed numbers.
Volker Diels-Grabsch fixed a link in the README file.
msm- added support for American Fuzzy Lop.
Annihil fixed an example in the README file.
Themercee noted a wrong URL in the README file.
Lv Zheng fixed a namespace issue with int64_t and uint64_t.
abc100m analyzed the issues with GCC 4.8 and proposed a partial solution.
zewt added useful notes to the README file about Android.
Róbert Márki added a fix to use move iterators and improved the integration via CMake.
Chris Kitching cleaned up the CMake files.
Tom Needham fixed a subtle bug with MSVC 2015 which was also proposed by Michael K..
Mário Feroldi fixed a small typo.
duncanwerner found a really embarrassing performance regression in the 2.0.0 release.
Damien fixed one of the last conversion warnings.
Thomas Braun fixed a warning in a test case and adjusted MSVC calls in the CI.
Théo DELRIEU patiently and constructively oversaw the long way toward iterator-range parsing. He also implemented the magic behind the serialization/deserialization of user-defined types and split the single header file into smaller chunks.
Stefan fixed a minor issue in the documentation.
Vasil Dimov fixed the documentation regarding conversions from std::multiset.
ChristophJud overworked the CMake files to ease project inclusion.
Vladimir Petrigo made a SFINAE hack more readable and added Visual Studio 17 to the build matrix.
Denis Andrejew fixed a grammar issue in the README file.
Pierre-Antoine Lacaze found a subtle bug in the dump() function.
TurpentineDistillery pointed to std::locale::classic() to avoid too much locale joggling, found some nice performance improvements in the parser, improved the benchmarking code, and realized locale-independent number parsing and printing.
cgzones had an idea how to fix the Coverity scan.
Jared Grubb silenced a nasty documentation warning.
Yixin Zhang fixed an integer overflow check.
Bosswestfalen merged two iterator classes into a smaller one.
Daniel599 helped to get Travis execute the tests with Clang's sanitizers.
Jonathan Lee fixed an example in the README file.
gnzlbg supported the implementation of user-defined types.
Alexej Harm helped to get the user-defined types working with Visual Studio.
Jared Grubb supported the implementation of user-defined types.
EnricoBilla noted a typo in an example.
Martin Hořeňovský found a way for a 2x speedup for the compilation time of the test suite.
ukhegg found proposed an improvement for the examples section.
rswanson-ihi noted a typo in the README.
Mihai Stan fixed a bug in the comparison with nullptrs.
Tushar Maheshwari added cotire support to speed up the compilation.
TedLyngmo noted a typo in the README, removed unnecessary bit arithmetic, and fixed some -Weffc++ warnings.
Krzysztof Woś made exceptions more visible.
ftillier fixed a compiler warning.
tinloaf made sure all pushed warnings are properly popped.
Fytch found a bug in the documentation.
Jay Sistar implemented a Meson build description.
Henry Lee fixed a warning in ICC and improved the iterator implementation.
Vincent Thiery maintains a package for the Conan package manager.
Steffen fixed a potential issue with MSVC and std::min.
Mike Tzou fixed some typos.
amrcode noted a misleading documentation about comparison of floats.
Oleg Endo reduced the memory consumption by replacing <iostream> with <iosfwd>.
dan-42 cleaned up the CMake files to simplify including/reusing of the library.
Nikita Ofitserov allowed for moving values from initializer lists.
Greg Hurrell fixed a typo.
Dmitry Kukovinets fixed a typo.
kbthomp1 fixed an issue related to the Intel OSX compiler.
Markus Werle fixed a typo.
WebProdPP fixed a subtle error in a precondition check.
Alex noted an error in a code sample.
Tom de Geus reported some warnings with ICC and helped fixing them.
Perry Kundert simplified reading from input streams.
Sonu Lohani fixed a small compilation error.
Jamie Seward fixed all MSVC warnings.
Nate Vargas added a Doxygen tag file.
pvleuven helped fixing a warning in ICC.
Pavel helped fixing some warnings in MSVC.
Jamie Seward avoided unnecessary string copies in find() and count().
Mitja fixed some typos.
Jorrit Wronski updated the Hunter package links.
Matthias Möller added a .natvis for the MSVC debug view.
bogemic fixed some C++17 deprecation warnings.
Eren Okka fixed some MSVC warnings.
abolz integrated the Grisu2 algorithm for proper floating-point formatting, allowing more roundtrip checks to succeed.
Vadim Evard fixed a Markdown issue in the README.
zerodefect fixed a compiler warning.
Kert allowed to template the string type in the serialization and added the possibility to override the exceptional behavior.
mark-99 helped fixing an ICC error.
Patrik Huber fixed links in the README file.
johnfb found a bug in the implementation of CBOR's indefinite length strings.
Paul Fultz II added a note on the cget package manager.
Wilson Lin made the integration section of the README more concise.
RalfBielig detected and fixed a memory leak in the parser callback.
agrianius allowed to dump JSON to an alternative string type.
Kevin Tonon overworked the C++11 compiler checks in CMake.
Axel Huebl simplified a CMake check and added support for the Spack package manager.
Carlos O'Ryan fixed a typo.
James Upjohn fixed a version number in the compilers section.
Chuck Atkins adjusted the CMake files to the CMake packaging guidelines and provided documentation for the CMake integration.
Jan Schöppach fixed a typo.
martin-mfg fixed a typo.
Matthias Möller removed the dependency from std::stringstream.
agrianius added code to use alternative string implementations.
Daniel599 allowed to use more algorithms with the items() function.
Julius Rakow fixed the Meson include directory and fixed the links to cppreference.com.
Sonu Lohani fixed the compilation with MSVC 2015 in debug mode.
grembo fixed the test suite and re-enabled several test cases.
Hyeon Kim introduced the macro JSON_INTERNAL_CATCH to control the exception handling inside the library.
thyu fixed a compiler warning.
David Guthrie fixed a subtle compilation error with Clang 3.4.2.
Dennis Fischer allowed to call find_package without installing the library.
Hyeon Kim fixed an issue with a double macro definition.
Ben Berman made some error messages more understandable.
zakalibit fixed a compilation problem with the Intel C++ compiler.
mandreyel fixed a compilation problem.
Kostiantyn Ponomarenko added version and license information to the Meson build file.
Henry Schreiner added support for GCC 4.8.
knilch made sure the test suite does not stall when run in the wrong directory.
Antonio Borondo fixed an MSVC 2017 warning.
Dan Gendreau implemented the NLOHMANN_JSON_SERIALIZE_ENUM macro to quickly define a enum/JSON mapping.
efp added line and column information to parse errors.
julian-becker added BSON support.
Pratik Chowdhury added support for structured bindings.
David Avedissian added support for Clang 5.0.1 (PS4 version).
Jonathan Dumaresq implemented an input adapter to read from FILE*.
kjpus fixed a link in the documentation.
Manvendra Singh fixed a typo in the documentation.
ziggurat29 fixed an MSVC warning.
Sylvain Corlay added code to avoid an issue with MSVC.
mefyl fixed a bug when JSON was parsed from an input stream.
Millian Poquet allowed to install the library via Meson.
Michael Behrns-Miller found an issue with a missing namespace.
Nasztanovics Ferenc fixed a compilation issue with libc 2.12.
Andreas Schwab fixed the endian conversion.
Mark-Dunning fixed a warning in MSVC.
Gareth Sylvester-Bradley added operator/ for JSON Pointers.
John-Mark noted a missing header.
Vitaly Zaitsev fixed compilation with GCC 9.0.
Laurent Stacul fixed compilation with GCC 9.0.
Ivor Wanders helped reducing the CMake requirement to version 3.1.
njlr updated the Buckaroo instructions.
Lion fixed a compilation issue with GCC 7 on CentOS.
Isaac Nickaein improved the integer serialization performance and implemented the contains() function.
past-due suppressed an unfixable warning.
Elvis Oric improved Meson support.
Matěj Plch fixed an example in the README.
Mark Beckwith fixed a typo.
scinart fixed bug in the serializer.
Patrick Boettcher implemented push_back() and pop_back() for JSON Pointers.
Bruno Oliveira added support for Conda.
Michele Caini fixed links in the README.
Hani documented how to install the library with NuGet.
Mark Beckwith fixed a typo.
yann-morin-1998 helped reducing the CMake requirement to version 3.1.
Konstantin Podsvirov maintains a package for the MSYS2 software distro.
remyabel added GNUInstallDirs to the CMake files.
Taylor Howard fixed a unit test.
Gabe Ron implemented the to_string method.
Watal M. Iwasaki fixed a Clang warning.
Viktor Kirilov switched the unit tests from Catch to doctest
Juncheng E fixed a typo.
tete17 fixed a bug in the contains function.
Xav83 fixed some cppcheck warnings.
0xflotus fixed some typos.
Christian Deneke added a const version of json_pointer::back.
Julien Hamaide made the items() function work with custom string types.
Evan Nemerson updated fixed a bug in Hedley and updated this library accordingly.
Florian Pigorsch fixed a lot of typos.
Camille Bégué fixed an issue in the conversion from std::pair and std::tuple to json.
Anthony VH fixed a compile error in an enum deserialization.
Yuriy Vountesmery noted a subtle bug in a preprocessor check.
Chen fixed numerous issues in the library.
Antony Kellermann added a CI step for GCC 10.1.
Alex fixed an MSVC warning.
Rainer proposed an improvement in the floating-point serialization in CBOR.
Francois Chabot made performance improvements in the input adapters.
Arthur Sonzogni documented how the library can be included via FetchContent.
Rimas Misevičius fixed an error message.
Alexander Myasnikov fixed some examples and a link in the README.
Hubert Chathi made CMake's version config file architecture-independent.
OmnipotentEntity implemented the binary values for CBOR, MessagePack, BSON, and UBJSON.
ArtemSarmini fixed a compilation issue with GCC 10 and fixed a leak.
Evgenii Sopov integrated the library to the wsjcpp package manager.
Sergey Linev fixed a compiler warning.
Miguel Magalhães fixed the year in the copyright.
Gareth Sylvester-Bradley fixed a compilation issue with MSVC.
Alexander “weej” Jones fixed an example in the README.
Antoine Cœur fixed some typos in the documentation.
jothepro updated links to the Hunter package.
Dave Lee fixed link in the README.
Joël Lamotte added instruction for using Build2's package manager.
Paul Jurczak fixed an example in the README.
Sonu Lohani fixed a warning.
Carlos Gomes Martinho updated the Conan package source.
Konstantin Podsvirov fixed the MSYS2 package documentation.
Tridacnid improved the CMake tests.
Michael fixed MSVC warnings.
Quentin Barbarat fixed an example in the documentation.
XyFreak fixed a compiler warning.
TotalCaesar659 fixed links in the README.
Tanuj Garg improved the fuzzer coverage for UBSAN input.
AODQ fixed a compiler warning.
jwittbrodt made NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE inline.
pfeatherstone improved the upper bound of arguments of the NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE/NLOHMANN_DEFINE_TYPE_INTRUSIVE macros.
Jan Procházka fixed a bug in the CBOR parser for binary and string values.
T0b1-iOS fixed a bug in the new hash implementation.
Matthew Bauer adjusted the CBOR writer to create tags for binary subtypes.
gatopeich implemented an ordered map container for nlohmann::ordered_json.
Érico Nogueira Rolim added support for pkg-config.
KonanM proposed an implementation for the NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE/NLOHMANN_DEFINE_TYPE_INTRUSIVE macros.
Guillaume Racicot implemented string_view support and allowed C++20 support.
Alex Reinking improved CMake support for FetchContent.
Hannes Domani provided a GDB pretty printer.

Thanks a lot for helping out! Please let me know if I forgot someone.

Used third-party tools

The library itself consists of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot!

amalgamate.py - Amalgamate C source and header files to create a single header file
American fuzzy lop for fuzz testing
AppVeyor for continuous integration on Windows
Artistic Style for automatic source code indentation
CircleCI for continuous integration.
Clang for compilation with code sanitizers
CMake for build automation
Codacity for further code analysis
Coveralls to measure code coverage
Coverity Scan for static analysis
cppcheck for static analysis
doctest for the unit tests
Doxygen to generate documentation
git-update-ghpages to upload the documentation to gh-pages
GitHub Changelog Generator to generate the ChangeLog
Google Benchmark to implement the benchmarks
Hedley to avoid re-inventing several compiler-agnostic feature macros
lcov to process coverage information and create a HTML view
libFuzzer to implement fuzz testing for OSS-Fuzz
OSS-Fuzz for continuous fuzz testing of the library (project repository)
Probot for automating maintainer tasks such as closing stale issues, requesting missing information, or detecting toxic comments.
send_to_wandbox to send code examples to Wandbox
Travis for continuous integration on Linux and macOS
Valgrind to check for correct memory management
Wandbox for online examples

Projects using JSON for Modern C++

The library is currently used in Apple macOS Sierra and iOS 10. I am not sure what they are using the library for, but I am happy that it runs on so many devices.

Notes

Character encoding

The library supports Unicode input as follows:

Only UTF-8 encoded input is supported which is the default encoding for JSON according to RFC 8259.
std::u16string and std::u32string can be parsed, assuming UTF-16 and UTF-32 encoding, respectively. These encodings are not supported when reading from files or other input containers.
Other encodings such as Latin-1 or ISO 8859-1 are not supported and will yield parse or serialization errors.
Unicode noncharacters will not be replaced by the library.
Invalid surrogates (e.g., incomplete pairs such as \uDEAD) will yield parse errors.
The strings stored in the library are UTF-8 encoded. When using the default string type (std::string), note that its length/size functions return the number of stored bytes rather than the number of characters or glyphs.
When you store strings with different encodings in the library, calling dump() may throw an exception unless json::error_handler_t::replace or json::error_handler_t::ignore are used as error handlers.

Comments in JSON

This library does not support comments by default. It does so for three reasons:

Comments are not part of the JSON specification. You may argue that // or /* */ are allowed in JavaScript, but JSON is not JavaScript.
This was not an oversight: Douglas Crockford wrote on this in May 2012:

I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't.

Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser.
It is dangerous for interoperability if some libraries would add comment support while others don't. Please check The Harmful Consequences of the Robustness Principle on this.

However, you can pass set parameter ignore_comments to true in the parse function to ignore // or /* */ comments. Comments will then be treated as whitespace.

Order of object keys

By default, the library does not preserve the insertion order of object elements. This is standards-compliant, as the JSON standard defines objects as "an unordered collection of zero or more name/value pairs".

If you do want to preserve the insertion order, you can try the type nlohmann::ordered_json. Alternatively, you can use a more sophisticated ordered map like tsl::ordered_map (integration) or nlohmann::fifo_map (integration).

Memory Release

We checked with Valgrind and the Address Sanitizer (ASAN) that there are no memory leaks.

If you find that a parsing program with this library does not release memory, please consider the following case and it maybe unrelated to this library.

Your program is compiled with glibc. There is a tunable threshold that glibc uses to decide whether to actually return memory to the system or whether to cache it for later reuse. If in your program you make lots of small allocations and those small allocations are not a contiguous block and are presumably below the threshold, then they will not get returned to the OS. Here is a related issue #1924.

Further notes

The code contains numerous debug assertions which can be switched off by defining the preprocessor macro NDEBUG, see the documentation of assert. In particular, note operator[] implements unchecked access for const objects: If the given key is not present, the behavior is undefined (think of a dereferenced null pointer) and yields an assertion failure if assertions are switched on. If you are not sure whether an element in an object exists, use checked access with the at() function. Furthermore, you can define JSON_ASSERT(x) to replace calls to assert(x).
As the exact type of a number is not defined in the JSON specification, this library tries to choose the best fitting C++ number type automatically. As a result, the type double may be used to store numbers which may yield floating-point exceptions in certain rare situations if floating-point exceptions have been unmasked in the calling code. These exceptions are not caused by the library and need to be fixed in the calling code, such as by re-masking the exceptions prior to calling library functions.
The code can be compiled without C++ runtime type identification features; that is, you can use the -fno-rtti compiler flag.
Exceptions are used widely within the library. They can, however, be switched off with either using the compiler flag -fno-exceptions or by defining the symbol JSON_NOEXCEPTION. In this case, exceptions are replaced by abort() calls. You can further control this behavior by defining JSON_THROW_USER (overriding throw), JSON_TRY_USER (overriding try), and JSON_CATCH_USER (overriding catch). Note that JSON_THROW_USER should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior.

Execute unit tests

To compile and run the tests, you need to execute

$ mkdir build
$ cd build
$ cmake .. -DJSON_BuildTests=On
$ cmake --build .
$ ctest --output-on-failure

Note that during the ctest stage, several JSON test files are downloaded from an external repository. If policies forbid downloading artifacts during testing, you can download the files yourself and pass the directory with the test files via -DJSON_TestDataDirectory=path to CMake. Then, no Internet connectivity is required. See issue #2189 for more information.

In case you have downloaded the library rather than checked out the code via Git, test cmake_fetch_content_configure. Please execute ctest -LE git_required to skip these tests. See issue #2189 for more information.

Some tests change the installed files and hence make the whole process not reproducible. Please execute ctest -LE not_reproducible to skip these tests. See issue #2324 for more information.

Note you need to call cmake -LE "not_reproducible|git_required" to exclude both labels. See issue #2596 for more information.

As Intel compilers use unsafe floating point optimization by default, the unit tests may fail. Use flag /fp:precise then.

Comments

How can I use std::string_view as the json_key to "operator []" ?

//as follow, this will fail as the key_type pof map is std::string_view std::map<string_view, bool> mv{{"111",true}, {"222", false}, {"333", true}}; nlohmann::json j4{mv};

//another: fail again, the std::string_view is the json_key nlohmann::json j5; std::string_view key = "my_key"sv; j5[key] = 100;
solution: proposed fix release item: :zap: improvement

opened by jencoldeng 94

Add a SAX parser

The library currently only supports DOM-like parsing. This does not scale when the input files are enormous (#927). I would like to discuss how a SAX-like parser could look like.

My proposal (heavily motivated by RapidJSON) is as follows:

struct SAX
{
    // a null value was read
    bool null();

    // a boolean value was read
    bool boolean(bool);

    // an integer number was read
    bool number_integer(number_integer_t);

    // an unsigned integer number was read
    bool number_unsigned(number_unsigned_t);

    // a floating-point number was read
    // the string parameter contains the raw number value
    bool number_float(number_float_t, const std::string&);

    // a string value was read
    bool string(const std::string&);

    // the beginning of an object was read
    // binary formats may report the number of elements
    bool start_object(std::size_t elements);

    // an object key was read
    bool key(const std::string&);

    // the end of an object was read
    bool end_object();

    // the beginning of an array was read
    // binary formats may report the number of elements
    bool start_array(std::size_t elements);

    // the end of an array was read
    bool end_array();

    // a binary value was read
    // examples are CBOR type 2 strings, MessagePack bin, and maybe UBJSON array<uint8t>
    bool binary(const std::vector<uint8_t>& vec);

    // a parse error occurred
    // the byte position and the last token are reported
    bool parse_error(int position, const std::string& last_token);
};

Some remarks:

All functions return a bool: true if the parser should continue or false if the parser should stop processing the input.
The proposal covers parsing of JSON, but also of CBOR, MessagePack, and UBJSON. Therefore, it contains extensions like array or object sizes as well as a binary type which do not occur when parsing JSON.
The idea is that the user would implement the above struct (we need to discuss whether we make all functions virtual, define a default implementation, etc.) and pass it to new parse functions, e.g. void parse_json(SAX &sax); or void parse_ubjson(SAX &sax);.

What do you think?

kind: enhancement/improvement solution: proposed fix

opened by nlohmann 79

json.hpp:5746:32: error: 'to_string' is not a member of 'std'
Hello. On Android i have this messages

json.hpp:5746:32: error: 'to_string' is not a member of 'std'

json.hpp:6911:36: error: 'strtold' is not a member of 'std'

android ndk have no to_strign realization
platform: android
opened by Ingener74 78
operator T() considered harmful
operator T() considered harmful

There's two subjects of importance that I'd like to tackle. This is the first one, I'll open another issue quickly (hopefully).

The problem

There's been several issues in the past related to the implicit conversion operator that the library provides. The current Readme demonstrates the following use-case:

// conversion: json -> person ns::person p2 = j;

This will call json::operator T() with T = ns::person, so no problems here.

You'd expect the following code to always work too:

ns::person p2; p2 = j;

And it works! Sometimes.

If ns::person has a user-defined operator=, it will break with the following message:

t.cpp: In function ‘int main(int, const char**)’: t.cpp:14:7: error: ambiguous overload for ‘operator=’ (operand types are ‘ns::person’ and ‘nlohmann::json {aka nlohmann::basic_json<>}’) p2 = j; ^ t.cpp:6:6: note: candidate: ns::person& ns::person::operator=(int) ns::person& operator=(int) { return *this; } ^~~~~~~~ t.cpp:3:8: note: candidate: constexpr ns::person& ns::person::operator=(const ns::person&) struct ns::person ^ t.cpp:3:8: note: candidate: constexpr ns::person& ns::person::operator=(ns::person&&)

Hard to understand that error, and it's not something that can be fixed by the library. It's triggered by the compiler before any template machinery on our side.

Now with such code:

void need_precise_measurement(Milliseconds); // later on json j = json::parse(config); need_precise_measurement(j);

It can fail in two cases:

Someone adds an overload for need_precise_measurement. Compiler error.

Someone changes the type of the argument to Nanoseconds. Runtime error at best.

Implicit conversions

Implicit conversions make the library pleasant to use. Especially when implicitely converting to JSON. That's because we have a templated non-explicit constructor with lots of constraints to correctly handle user types. There's also a single type to convert to: nlohmann::json, so everything works.

However, when converting implicitely from json, it's the complete opposite. If the compiler cannot decide which type it should implicit convert the nlohmann::json value to, you get a compiler error.

And it could happen in a codebase months after writing the code, (e.g. when adding an operator= to a type).

In the end the only consistent way to convert from a json value is to call json.get<T>.

Proposed change

I propose to simply and completely remove operator T().

It will obviously break code, so it can only be done in a major version.

Of course this change cannot be adopted right away, so I propose to add a deprecation warning inside operator T(), as we did for basic_json::basic_json(std::istream&) overloads.

Then it would be reasonable to remove it in a future major version.
solution: proposed fix release item: :sparkles: new feature
opened by theodelrieu 75
Soften the landing when dumping non-UTF8 strings (type_error.316 exception)
When dumping a json object that contains an std:string we could be thrown the type_error.316 exception if the string contains invalid UTF8 sequences. While this sounds like a reasonable thing to do, it actually causes more problems than it fixes. In all the cases where user-entered (unsafe) strings end up stored in nlohmann::json objects the developer now has to "do something" before assigning a string value to some nlohmann::json variable. This effectively renders the whole string assignment functionality unsafe and defeats its purpose.

Below is the wrapper code I had to write in order to investigate the random crashes my application went through due to the 316 exception.

// Declaration: std::string dump_json(const nlohmann::json &json, const int indent =-1, const char* file = __builtin_FILE(), int line = __builtin_LINE()) const; // Definition std::string MANAGER::dump_json(const nlohmann::json &json, const int indent, const char* file, int line) const { std::string result; try { result = json.dump(indent); } catch (nlohmann::json::type_error& e) { bug("%s: %s (%s:%d)", __FUNCTION__, e.what(), file, line); } return result; }

This led me to the discovery of the code in my application that was sending json formatted log events to the log server. The log event has to store user entered data and I would expect the dump function to deal with invalid UTF8 sequences.

If I have to use my json dump wrapper everywhere in my application code then of what use is the original dump function to begin with? What is more, I'd actually have to enhance the wrapper function to iterate over all strings stored in the json object and do something about the possible invalid UTF8 sequences. Not very convenient.

Therefore, I would propose the default behavior of the dump function to simply ignore (skip or replace) invalid UTF8 sequences and NOT throw. Or perhaps add a nothrow parameter to the string assignment = operator.

If left like that, I probably won't be the last developer who assumed that the dump method is safe to use. After all, if the lib allows me to assign a value to the json object then how can it be that it lets me assign values that later invalidate the whole json? This is illogical.

// nothrow assignment would look like this nlohmann::json j_nothrow = (std::nothrow) "\xF0\xA4\xAD\xC0"; // Does not throw. // I am not 100% sure if this can be done, but since the `new` operator can have such // a parameter I would suppose the assignment operator = could also be customized // like that. std::string dumped = j_nothrow.dump(); // Never throws, just works. nlohmann::json j_throw; try { j_throw = "\xF0\xA4\xAD\xC0"; // Throws immediately. } catch (nlohmann::json::type_error& e) { // handle the invalid UTF8 string }

One more thing. Why not include the file and line from where the exception originated in the exception description? You can see in my above wrapper function how I am using __builtin_LINE() and __builtin_FILE() to store the file and line information from where the wrapper call was made. It is super useful when debugging and exception description is all about debugging.
solution: proposed fix release item: :sparkles: new feature
opened by 1Hyena 67

Custom type registration : instrusive API

Currently, the API for registering custom types is as follows:

using nlohmann::json;

namespace ns {
    void to_json(json& j, const person& p) {
        j = json{{"name", p.name}, {"address", p.address}, {"age", p.age}};
    }

    void from_json(const json& j, person& p) {
        j.at("name").get_to(p.name);
        j.at("address").get_to(p.address);
        j.at("age").get_to(p.age);
    }

It would be great if there was a MACRO-style registration a bit like what msgpack-c uses:

struct person 
{
   std::string name;
   std::string address;
   int age;
   MSGPACK_DEFINE_MAP(name, address, age);
};

or yas:

struct   person
{
   std::string name;
   std::string address;
   int age;
    YAS_DEFINE_STRUCT_SERIALIZE("person", name, address, age);
};

struct   person
{
   std::string name;
   std::string address;
   int age;
};
YAS_DEFINE_INTRUSIVE_SERIALIZE("person", name, address, age);

kind: enhancement/improvement solution: proposed fix release item: :zap: improvement

opened by pfeatherstone 62

Refactor/split it
Here it is.

This PR is the follow-up of #643, and the second phase of my planned refactoring (there will likely be one more, but we shall discuss it in a separate thread, since it requires naming/structural changes).

I've added a tool to amalgamate the library into a single header (like Catch does), @nlohmann pointed out this was necessary.

There is a new rule in the Makefile: single_include, that builds, and executes the tool.

The output is located in the single_include folder, at the root of the repo.

The only requirement is that every included file that is part of the library must be with the following style:

#include <will_not_be_inlined.hpp> #include "will_be_inlined.hpp"

Each include must be done with a path relative to the source folder:

// detail/conversions/from_json.hpp #include "detail/value_t.hpp" // good #include "../value_t.hpp" // NOPE, not refactor-proof

I've also added one test for each source file (except json.hpp), to check that we didn't miss any include. This will be helpful for future refactoring.
opened by theodelrieu 61
How to make sure a string or string literal is a valid JSON?

I'm gonna be sending strings to the parser that might or might not be valid JSONs and I need a way to check they are. I'm programming for a Nintendo 3DS, but using try to catch an exception does not work and the application hangs anyway if it finds an error while parsing. What can I do?
kind: enhancement/improvement solution: proposed fix

opened by ghost 59

Please add a Pretty-Print option for arrays to stay always in one line

Please add a Pretty-Printing option for arrays to stay always in one line (don't add lines) if dump() parameter > -1 or std::setw()) is set. So that only other JSON types than arrays are expanded.

Example:

json j;
j["person"]["name"] = "Glory Rainbow";
j["person"]["age"] = 61;
j["person"]["mind"] = "Easy going";
j["color"]["month"] = { 1, 3, 5, 7, 8, 10, 12};
j["color"]["order"] = {"red", "orange", "yellow", "green", "blue", "indigo", "violet"};
std::cout << j.dump(4);

Wanted output:

{
    "color": {
        "month":  [1, 3, 5, 7, 8, 10, 12],
        "order": ["red", "orange", "yellow", "green", "blue", "indigo", "violet"]
    } ,
    "person": {
        "age": 61,
        "name": "Glory Rainbow",
        "mind": "Easy going"
    }
}

Thank you!

kind: enhancement/improvement solution: wontfix

opened by mireiner 59

Fail to build when including json.hpp as a system include
What is the issue you have?

When including json.hpp if the include directory is marked as a system include (-isystem rather than -I) it will fail to build

I have to turn on CMAKE_NO_SYSTEM_FROM_IMPORTED and force the include path to be used as -I instead of -isystem. -isystem is used whenever nlohmann is provided as part of an imported CMake target. This happened to me due to using nlohmann from hunter with LLVM for Windows.

Please describe the steps to reproduce the issue. Can you provide a small but working code example?

Sample CMake script

project(test) cmake_minimum_required(VERSION 3.14) add_executable(test main.cpp) target_include_directories(test SYSTEM PRIVATE "<path/to/nlohmann/json>")

Simple C++

#include <nlohmann/json.hpp> int main() { // Don't even have to call anything return 0; }

What is the expected behavior?

Program compiles successfully

And what is the actual behavior instead?

A ton of errors along the line of error: expected '>'enable_if_t<is_detected<mapped_type_t, ConstructibleObjectType>::value and

Which compiler and operating system are you using? Is it a supported compiler?

Clang 9.0.0 but the same behavior occurs with 8.0.0/8.0.1

This is with LLVM for Windows and happens with the ClangCL toolset for VS2019 and the Ninja generator in CMake 3.15+

Did you use a released version of the library or the version from the develop branch?

Version 3.6.1 and 3.7.0 release versions have the same problem

If you experience a compilation error: can you compile and run the unit tests?

Nope
kind: bug solution: proposed fix release item: :zap: improvement
opened by Honeybunch 55
CBOR byte string support

Currently, the CBOR feature of the library only supports writing strings out as UTF-8 and doesn't support byte arrays as described in the CBOR standard. I'd like to implement COSE on top of this library, but in order to do that, byte string support is needed.

I'm happy to submit a pull request for this, but I wanted to check in advance if this is something you'd be open to
solution: proposed fix aspect: binary formats

opened by daviddesberg 54
error: expected initializer before ‘<’ token
Description

When using the single include header (https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) I get the following error during compilation error: expected initializer before ‘<’ token in line 5323. Sorry if it's an easy fix, I don't have much experience with C++. I'm using g++ together with the latest CUDA compiler nvcc under WSL. Edit: does not work using C++20, C++17 (probably below as well) compiles flawlessly

Reproduction steps

Include "json.hpp" in any header file

Expected vs. actual results

Expected: Successful compilation Actual: No compilation

Minimal code example

No response

Error messages

No response

Compiler and operating system

g++ (Ubuntu 12.1.0-2ubuntu1~22.04) 12.1.0 | Cuda compilation tools, release 12.0, V12.0.76 Build cuda_12.0.r12.0/compiler.31968024_0

Library version

version 3.11.2

Validation

[X] The bug also occurs if the latest version from the develop branch is used.

[ ] I can successfully compile and run the unit tests.

kind: bug
opened by RerikOp 0
Fix CI issues
I looked a bit at the ci_test_compilers_clang (10) issue. This PR did not change the affected test and it worked in earlier builds.

It seems the compiler and changed to a newer version.

old:

Compiler: clang version 10.0.0; Target: x86_64-unknown-linux-gnu; Thread model: posix; InstalledDir: /usr/local/bin

new:

Compiler: Debian clang version 10.0.1-++20210313014605+ef32c611aa21-1~exp1~20210313125208.190; Target: x86_64-pc-linux-gnu; Thread model: posix; InstalledDir: /usr/bin

Pull request checklist

Read the Contribution Guidelines for detailed information.

[ x] Changes are described in the pull request, or an existing issue is referenced.

[ ] The test suite compiles and runs without error.

[x ] Code coverage is 100%. Test cases can be added by editing the test suite.

[x ] The source code is amalgamated; that is, after making changes to the sources in the include/nlohmann directory, run make amalgamate to create the single-header files single_include/nlohmann/json.hpp and single_include/nlohmann/json_fwd.hpp. The whole process is described here.

S tests
opened by barcode 2

The library can not parse JSON generate by Chome DevTools Protocol

Description

The library throws exception when I try to parse JSON message produced by Chrome browser via Chrome DevTools protocol. I have no idea whether Chrome breaks any standards or not, but Chrome is standard de-facto, so at least any flag that will make the library compatible with Chrome may be good idea. I also can visualize the JSON with Visual Studio, Notepad++ and some other tools, so this format is OK for other widely used tools.

Reproduction steps

I add the code sample (Visual Studio 2022 native unit test). I just call json::parse for some JSON file generated by Chrome browser.

Expected vs. actual results

I expect that if Chrome, Visual Studio, Notepad++ can parse the JSON, nlohmann::json should also supply a way to do so. You can download the file that contains target JSON here: data.json

Minimal code example

#include "pch.h"
#include "CppUnitTest.h"

#include <format>
#include <fstream>
#include <string>

#include <nlohmann/json.hpp>

using namespace Microsoft::VisualStudio::CppUnitTestFramework;

namespace JsonTest
{
	TEST_CLASS(JsonTest)
	{
	public:
		
		TEST_METHOD(Nlohmann)
		{
			using namespace nlohmann;
			using namespace std;
			try
			{
				fstream json_reader(R"__(c:\data.json)__");
				json json_data = json::parse(json_reader);
			}
			catch (const exception& error)
			{
				Logger::WriteMessage(format("Can not parse JSON file. {}", error.what()).c_str());
			}
		}

	};
}

Error messages

Can not parse JSON file. [json.exception.parse_error.101] parse error at line 1, column 7198: syntax error while parsing value - invalid string: surrogate U+D800..U+DBFF must be followed by U+DC00..U+DFFF; last read: '"\u001f\b\u0000\u0000\u0000\u0000\u0000\u0000\u0003s~EJvoCJ\n$A\u0011I)Y~2Ye4\u017cs';;O;yHT\u06f4m\u00f2\r{tk\r\u000ea97 8]\u0013\u000e!<32p]9\u0004Yw\u000eZN'w&FkwQL\u0005fx#k4\u00188=:\u001fvXc'-x,\b\\sl\u0006\r\u00181L\u000f${\u00159K\u0005ND\"QS\u0001$\u0007^\u428d-\"8,HBz\u0001\u001ai\u001f&\u001ag/xE\ucaae\u0006 9\"9X*-\u03d0x~MvLgy\u0225V-zz-d~2cI\u00a3\u001fiv~dDD\u0011~\u00073\u0539da1\"\u06c6\u000eT\u0019N3?c\u000b9-\u0006\u001b\u000f}r;0\u0016\u0329\u0007a16G`\u001c\fLn\u0006\u001b#\u00160gFccn\u001a~\u000f,%p]{i\u001f5-hK\u069c\u04b1\rGm'N\u0014\u0001\u0011i=6\u0002ao\u00028)<\u000ft\u0013sJ32g\u04f0#\u59dd\u03d4\u001dMFwyl|&2\u001a`A\u0006\u0010=\u0341\u0003Xp;>Fg\u00d1e;dd\u001fgp\[email protected]&L yw\u0007\u0002/\u053dtyr9\n[$:1r`\u0307\u001e\f\u0546<tg+\u0019\u0002h4e!,Y+e\u0002B~\[email protected]\u001dnGI\u001b\u0001j^\u001e\\\u000b~\u0003#\u0007op\rfr\u05a8gI0w\u0019J\u001e\u0751/61kR$4pesK}\u0016IH\"\u030d(\u04c8I}S?\u02dd:\u0003\\\"\n\u0015l\u0732PW \u001351, ?\u000b3_,[email protected]\u001c\u0010r\u00109(eK\u0013\u0002)8K\u000fI]a\u0006|1?sjU%d+meYFQu\u02fb\"!5\u000fv\u000e.\u001aN\u05c4\u0012\u0010\u0014Rx\u03627`m\u0010=\u001f!zr}Y\u0004>-z\u00039O.\u0335|\u001f{[email protected]\\N\nf54&D}0co1f\u00160b M\u0013v`,%!X_\u000bB=<\u001aB\u0014\f/]3\u0010e/\u0002\u001eda\u0011D\u0011E5\u0233D\u001e[$\u001aH$:\u001bF#\b\u0014\rB\u03c5\",A\u001e%T\u0002\u0004C\u000e}84sqB5\u000e\u01e9\u0013\u0012y\u001e[$HdA$C\u0003Y\u01e2\b\u0016?7\fY\n8gB\u001eZ\"jg=W{M`\"\u03f1;O\"aQ$\nr\u001f^|\u0006g_m8\"\u001bQ`5_> y\u000eI\u000b\u001e>o\u0004\u0002)J<isA1sRBL#\u001esKM'Su\u0010\u001a3q\u001f+\u012ex\u001eOx\u0016<\u001eA\[email protected]\\$Qp\u001anT\u0001?F\u001cL?<FCnW+&WR~n\u0004\b)\u0011y\u0018ae\u0018LkCPB\u0013bL\u0017CB9\u0003?,1<Af\u001b^K&\u0002\u0018aL3\u0393G0q?<\u0000\u0006N\u0011/B\fe\u02db\"YX\u000fn\u000f\u0000\u00135cTt\u0018\u0018<$\u000fJ'\u0002w\u0267\u0120?j7\u0006T\u001d\u0007s\u001c\u001c\u0004Q\u0016b\u00060\b_:=--\u0019Y\u0018\u0000W\u0015C\u06547D\u0012zYsH\u0014L\u0011~^\u0015\u001etF<\b33\u0011mhT\u020d\u0000> a\u000e\u001di|2[ \u0013\u001a\u0011i`#\u000b1:\u0000\f$\u05bdxsirs\u0005W9\fL*\u07d82o\u001bb9\fh&r`\u28c8e\u0012+\f \u078b\u001a\"YA{XXJ\rDItSX2\u000by\u0006\u0014\u0012l\u0015\[email protected]`p]4CE3\u0012  Dwq7o33\u02c4/[TYy\u0016n\u0014J\u0018#Bg4\u01fa.s\u0016S\bKaZ0\u0010y)h\bxh\b,\u0018$=\u0000\"yR\u0016\u000f\"\b`qlZ:Q\r\u0016\u000f)\u00042Y&'b\u001a\u0002Z\t2\u0012\u0214\u0000\u0011+F\u0000`6\\f,\[email protected]\u00195_24|M#3#\u0003VK\u030aays\u00018\u0002uw!\u04cf[B8),MKL\u000bE\u0006CQ&\u001f\u0552\u001c\u0014\u001f6Rz\u0004K3J3TBz\u0015\u001a6\u0018\tVt\u001eOWd\\R71!\"X\\N^\u0014O\u000f\u0019\"\u0003\u0013syCq0<o\u0002\u0013\u0003X4(Y\u000e\u0013J\u0002\u0011nHA\u03a2\"N\u000f\u0013X>x&\u000bVe\u0014X\u000fY\u0002:< `fr\n\u0017v\u0000WQ\u001b?\u0001b\u00109E\u0000\u0006^\\7\b~+cj3g\u0014Rq\b~X7\u00163XlV~\u0003<\u000e\"CV7tSX\u0013\u0017\u0018'\u001c\fR\u0004sj\u0004\u001ea\u001aeF?\u0011zmKq0+^Z8\u000b]\u0017bNDVN?\u0019H\u0014s\u0005\u001bE\bbq#3\u00069\u0411/<\bb\u0017=R\u0006i.Ae$\u0003K,\u0005\u000f6\u001a,SnW\u001cpi\u0007{+\\#\u0016!_\u001a,|\u0011(tw\u0011wA\u0006qNEE9+\u071aPDE\u0756\u0720\rb\u0018pjC\u0019[Ck`)b=Ig\u0016 \u0152g\u0000_\u0014:\u0018,Y`T0z\u0398[qd\u000e\u0006NB%\u000f\u0000X\u0012,\[email protected]'I,\t3\bQ\u0013~\u001aJ\u0016X!7t\u0012%\u001am*S\u001fj\f\u0674N3Qiij\u0015\"\"\r\u0011q\u001c\u001cm3\b\u0006*\u0012J:B+f\u0010V\u0007a\u0005HS_.!\u0011mbH![\u001b\u0142gi955UE*\\%baq3t~!c,t5Ex2hV$\u0014S*`\u001bwr\b\u02e0Y\u0010\u0005\u0018\u0015sV_k^<\u00166M\u0002^cyK\u000f\u0017\u001emg\u0004\u0016F~\na\u06cbP\u00152<}\u0012x\tx\u015f\tX9\u000fS\u001d<5X<t!LD\u000e{\u0004:4A\u0293\u001bE1\u01dc5K.{=\u0000,X|pdXh\bvY\u0006S(@p\u0002\u02f6\u0001\u00032\u0016eHX\u0016E\u0440!\u0540+i9_50I\u0012&\u0088D\u0010#\u017c-1_rJ\u0018\u0018Q\u0019uSn19O0\bB:\f20+o\u0018qO\b.H'\u0011a\u0014\\\u0007Z\u0002#\t\u0735\u0007md\u0006M,%\u0011`R\u000f\u0003HHD4\u07390\u001dXc,\u01a9&$*D8$1X\\\u05f0\"@\u0016h4a3\u00d0~\u0001G\b\u0004eWJ~IXPLG+\u0001L[!\fh\u0000\u6ee2R\u0014\u0011\u0000\u607f{`\u026aYHN\u0005E\u0002s\n3RJ\u0014Ad+\u000e\u0011\u0017l\u0011`gIl7\u0015\u00129c\u0018ha\u062er9701\u0002O\u001dE\[email protected]*me\u001c6\u0006I4B`\u0004Q)F\u001a\u0003\u00199\u0019\bFY\u000bF\u03ee\u0014G\[email protected]\"\u0004k\u0000BG\u001d\u0004+S&T$1\u0014u\u0015P,\f9A\u000eQ\u0001\u0007~&V\r\"Z\u0004\u0015J4C]V \u000e&S\u0739\u0631-u!mM5O\n\u001bZE!\u031eW\u0241UD:` J\u000b\t8\"?%rM\u0004\u0002\u0001C<\u0005\u001c\u0198eA\u001d08\u0010\u0011\u0000\u000bJ8 \u001a*TRj;Wv\bD\u001a`\u04e9[`\u0013`?R\u7498&\nVVGs;sC\u00043\u001a\u0012\u0017,b\u0018Qn,eJ+=i<6v%{!^o\u0620F\t[J.\u0013~P\u001f\u000bJ,\u0002\u05f2]h\u000brkWnu\u0000\u001dF\u07c4\u001bjkTd\u0005lzsj\u000b\nW<D(\nDM\u0018cx\u000f\u0003-+tgp\u0001Y\u001eD).\u0772v/9UT\u0016|\u0013'\u0011.CA\u0017eb0#4\u0015\u001d\\\u0015ki\u042eMSa<j\u0002b)7Kg\u0001\u03da\u0016n.\u001e njq]>KXS=mg\bjs\u0616\u0014sj7\u0005?h\u4008]\u0015^\[email protected]\"\u000eJ<p_gh\u04ba\u042d\u06b1!>Vr\u000bh\u5f0f\\o\"+g\u001f)!\u001a\u0018\u0015Qm\u06f4\rp;\u000fmO\u0269 p h\u00027V\feU\u0016\u00012\u0615lve+\u0010\u0018nVX\u0016\u04e36m}|'1J6\u03a9A 1J\u0165\u0016k*H8C\u0005*\u0003\u0012[Sf0}GuJpq\u00efQRI\u001cvT\u0330Y\u0006\u072a`\fZ5\u000eLVNY\u001eGj\u0007\u0018t\u0000Ll1;F[[email protected]\u0014*i]YW\u0019L6\u0018t\u0003JAO:.\f}*Um6/\u0003Yn\u0003\\@<^\u0013;YJ\u0014lR8+=\u0011<6b\u0018Ta$:\f%MAE\u0469`.\"5\nw~$-\u001ej<Ss\nr\u0727\u0004%{y.i\fzG.Y\u0013m*\u00044euj\b7S'1\fUA\u0189'8p\u0002\u0018]:P\u19a8_z'ks\u000eX\u001f\u001a\u001eG\u06b85)\u032dnMtJgYm&R>`K\u01673Bm%\u0016\u0016\u001dLbc;\u0010nY-\u001a!\u0003\[email protected]\u04e8vd\nW\u0011$.:\u0006a\u06a5w\u5c3c[SljK}``X4#\u0006C,\u0002 g\u0272<\"4\u0690\nI6~#\u0010\u0010\u0541\u0004pVP;j\u00154=O\uf8ca\f\u0019SmbKc\u0000(\u079d\u000b|\b\u0001!NE\"\u00158[:C\u000b\u0000H\t\u056fqkp<r<u3MzS\u0466XjD\u0017[YG\u001f\u0010\u05de\\p3\\G9\u001d~HVwx8eYB]jhH/ \r`=IL<K\uc9b9\t\u416d/W[\u001cy\bZ*]d(`\u0013X\u0001YVDy\\\u0000\u0016\\5q7U\u0002^N\u0019z\u0016\u0000\[email protected]\rDA2LSE\u0007\b\u0018\r\u0001P4\"[email protected]!l&\u0017i\"Q\u0012P`qT\u0000C`=9SlH\u00150m.:y.)(\u000fBm\ud81d\"'

Compiler and operating system

Visual Studio 2022, Windows 11 Pro.

Library version

3.11.2

Validation

[ ] The bug also occurs if the latest version from the develop branch is used.
[ ] I can successfully compile and run the unit tests.

kind: bug

opened by goodguysoft 3

Typo in `cmake/test.cmake`

Description

At line 260 in cmake/test.cmake there is this code

        include(CheckTypeSize)
        check_type_size("size_t" sizeof_size_t LANGUAGE CXX)
        if(sizeof_size_t AND ${sizeof_size_t} EQUAL 4)
            message(STATUS "Auto-enabling 32bit unit test.")
            set(${build_32bit_var} ON)
        else()
            set(${build_32bit_var} OFF)
        endif()

The conditional check

        if(sizeof_size_t AND ${sizeof_size_t} EQUAL 4)

The first condition if(sizeof_size_t is always TRUE, since it is comparing against the string value "sizeof_size_t". To check if the string is empty (meaning check_type_size could not return a value for size_t) it should be

        if(${sizeof_size_t} AND ${sizeof_size_t} EQUAL 4)

If for some reason the size of size_t is unknown (for example, using exotic toolchains where stddef.h might not be visible during the initial cmake evaluation) this will cause the invocation of cmake to fail.

Reproduction steps

Replace the call to check_type_size with

set(sizeof_size_t "")

Expected vs. actual results

Running cmake . should not fail.

Minimal code example

No response

Error messages

if given arguments:

    "sizeof_size_t" "AND" "EQUAL" "4"

  Unknown arguments specified



### Compiler and operating system

gcc 11.2.0, Linux

### Library version

3.11.2

### Validation

- [X] The bug also occurs if the latest version from the [`develop`](https://github.com/nlohmann/json/tree/develop) branch is used.
- [ ] I can successfully [compile and run the unit tests](https://github.com/nlohmann/json#execute-unit-tests).

kind: bug

opened by m-hilgendorf 1

Prevent memory leak when exception is thrown in adl_serializer::to_json
(problem described in issue #3881)

There is a memory leak when throwing inside an adl serializers to_json method.

[x] Add unit test

[x] Implement fix

[x] Fix Ci

Pull request checklist

Read the Contribution Guidelines for detailed information.

[x] Changes are described in the pull request, or an existing issue is referenced.

[x] The test suite compiles and runs without error.

[x] Code coverage is 100%. Test cases can be added by editing the test suite.

[x] The source code is amalgamated; that is, after making changes to the sources in the include/nlohmann directory, run make amalgamate to create the single-header files single_include/nlohmann/json.hpp and single_include/nlohmann/json_fwd.hpp. The whole process is described here.

L tests
opened by barcode 7
RTTI dependency added by std::any
Description

When compiling with -fno-rtti using clang, ninja on VS 2022 17.4.3 the build will fail.

This line seems to be causing the issue:

#if defined(JSON_HAS_CPP_17) #include <any> #include <string_view> #endif

Including any requires rtti to be on.

This error was produced using ninja and the VS 2022 17.4.3 clang compiler.

C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.34.31933\include\any(22,2): error GDF32A4F7: class any requires static RTTI. #error class any requires static RTTI. ^

Reproduction steps

Build using ninja and -fno-rtti and the VS 2022 17.4.3 clang compiler.

Expected vs. actual results

Expect: compilation successful Actual: #error class any requires static RTTI.

Minimal code example

No response

Error messages

No response

Compiler and operating system

MSVC 17.4.3

Library version

3.11.2

Validation

[ ] The bug also occurs if the latest version from the develop branch is used.

[ ] I can successfully compile and run the unit tests.

kind: bug
opened by vongkitt 7

Releases(v3.11.2)

v3.11.2(Aug 12, 2022)
Release date: 2022-08-12 SHA-256: 665fa14b8af3837966949e8eb0052d583e2ac105d3438baba9951785512cf921 (json.hpp), e5c7a9f49a16814be27e4ed0ee900ecd0092bfb7dbfca65b5a421b774dccaaed (include.zip), 8c4b26bf4b422252e13f332bc5e388ec0ab5c3443d24399acb675e68278d341f (json.tar.xz)

Summary

This release fixes some bugs found in the 3.11.1 release. Furthermore, the of the namespace library has been re-structured.

All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug Fixes

Fix the value function which was broken for strings, size types, and nullptr in release 3.11.0. #3652 #3655 #3663

Fix the json_fwd.hpp header to be self-contained and add it to the single-header release. #3656 #3679 #3687

Fix regression that broke using json_pointer as key in associative containers. #3680 #3685

Add missing constraint to deprecated JSON Pointer overloads of contains and at. #3658 #3681

Fix comparison between json_pointer and strings with == and !=. These comparisons worked in 3.10.5, but were broken in 3.11.0 and 3.11.1. #3654 #3664

Fix to_json conversion of std::vector<bool>::reference and std::vector<bool>::const_reference for STLs where these are the same as basic_json::boolean_t& and basic_json::boolean_t, respectively. #3677 #3678

:zap: Improvements

Restructure inline namespace and allow version component to be disabled. See documentation. #3683 #3696 #3697 #3698

Avoid heap allocations in BJData parser. #3637

:hammer: Further Changes

Documentation

Publish documentation on every push to develop branch. #3660 #3673

Add missing examples for the public API. #3672 #3686

Fix typo in json_pointer documentation. #3692

Community

Add a badge for the Discord chat to the README file. The goal of that additional communication channel beyond the existing ones is to quickly coordinate between the contributors. #3651

Complete contributor list. #3662 #3670

CI

Remove the macos-10.15 image from the CI as it is removed by GitHub Actions. #3612 #3615 #3626

Remove hardcoded paths in Ubuntu workflow. #3626

Only trigger AppVeyor builds if relevant files have been changed. #3626

Fix CodeQL warning. #3626

Harmonize naming of GitHub Actions jobs. #3661

Add labeler action to automatically add PR labels based on the changed files. #3671 #3674 #3675

Lint API documentation in the CI. #3672

Add local LGTM configuration and suppress warnings on third-party scripts. #3643

:fire: Deprecated functions

This release deprecates comparing JSON Pointers with strings via operator== and operator!=. To compare a json_pointer p with a string s, convert s to a json_pointer first and use json_pointer::operator== or json_pointer::operator!=. #3684

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

The function iterator_wrapper is deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The implicit conversion from JSON Pointers to string (json_pointer::operator string_t) is deprecated. Use json_pointer::to_string instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(286.92 KB)
include.zip.asc(833 bytes)
json.hpp(886.58 KB)
json.hpp.asc(833 bytes)
json.tar.xz(107.30 KB)
json.tar.xz.asc(833 bytes)
json_fwd.hpp(6.12 KB)
json_fwd.hpp.asc(833 bytes)
v3.11.1(Aug 1, 2022)
Release date: 2022-08-01 SHA-256: 9279dc616aac67efce68967f118051b50236612b90572e059783d368bd78687e (json.hpp), 9c15ca7806f863872452bfbc85fee6d1c9868117e3ea5e00a204ae961a2e1ae7 (include.zip), e6dd39f8f2da9cab11de2212acdd40b1cc1aafbe09da8c92933b911d19da3302 (json.tar.xz)

Known issues

#3652 Regression: call to member function 'value' is ambiguous

#3654 Regression: no match for 'operator!=' comparing json_pointer and const char */string_t

#3655 Regression: .value<size_t> is compilation error

All issues are fixed in the develop branch and will be part of the 3.11.2 release.

Summary

Version 3.11.0 moved the user-defined string literals (UDL) into namespace nlohmann::literals::json_literals (see documentation). Unfortunately, this namespace was not imported to the global namespace by default which broke code. This release fixes this bug.

All changes are backward-compatible. See release notes of version 3.11.0 for more information on other features.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug fixes

Set default value of JSON_USE_GLOBAL_UDLS and the CMake options JSON_GlobalUDLs to 1 to import the user-defined string literals from the nlohmann::literals::json_literals namespace into the global namespace by default. #3644 #3645 #3646

Source code(tar.gz)
Source code(zip)
include.zip(284.44 KB)
include.zip.asc(833 bytes)
json.hpp(875.64 KB)
json.hpp.asc(833 bytes)
json.tar.xz(105.84 KB)
json.tar.xz.asc(833 bytes)
v3.11.0(Aug 1, 2022)
:bug: Unfortunately, this release introduced a bug that breaks existing usages of the user-defined string literals (UDL). This is fixed in version 3.11.1.

Release date: 2022-08-01 SHA-256: eb73896e9ce706ae6a62ce697dc8aca214840f70d8281779a6ea0cabe3afab3f (json.hpp), b4789050cacd110faf8b100cee82af19ad0b4d3249625f6582a60eeeb80c84a7 (include.zip), 5c8f7a4d9e9c0d565e71b6e5b0b3a12f784ffbf142e1ddc7ba86002cefb4c6ee (json.tar.xz)

Summary

Version 3.11.0 is one of the biggest releases (in terms of closed issues and merged pull requests) ever. It brings:

String view support for all functions working on object keys (e.g., at or operator[]), avoiding unnecessary allocations.

BJData as the fifth supported binary format besides BSON, CBOR, MessagePack, and UBJSON.

Better C++20 support to make the library integrate more smoothly with newer codebases.

Better support for avoiding problems when multiple versions of the library are used in the same project.

Even better and more extensive documentation and examples.

More tests for edge cases like 32-bit support, C++20 features, using the library with ICPC, or after including <windows.h>.

All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:sparkles: New Features

Allow to use std::string_view as object keys in at, operator[], value, erase, find, contains, and count to avoid unnecessary allocations. #3423, #1529, #3558, #3564

Add support to read and write the UBJSON-derived Binary JData (BJData) format (see documentation). #3336, #3461, #3463, #3475, #3479, #3493, #3491, #3492, #3490, #3500, #3502, #3503, #3505, #3513, #3514, #3519, #3523, #3541, #3543

:bug: Bug fixes

Allow creation of ordered_json objects from initializer lists. #3342, #3343, #3370

Fix failing tests when compiling with C++20 and add support for operator<=>. #3207, #3446, #3472

Fix comparison-related compilation problems in C++20 on GCC 12. #3138, #3379

Make iterator satisfy std::incrementable. #3331, #3332

Exclude std::any from implicit conversion. #3428, #3437

Fix constraints on from_json() for strings. #3171, #3267, #3312, #3384, #3427, #3312, #3620

Make iterators usable with <ranges> and range-v3. #3130, #3446

Fix comparison of NaN values with json to behave like float. #3409, #3446

Add operator<<(json_pointer) to fix a regression after the 3.10.0 release. #3600, #3601

Fix JSON Patch to not create missing parent objects. #3134, #3199, #3628

Re-add value_type detection to distinguish string types (was broken in releases 3.10.4, and 3.10.5). #3204, #3333, #3604, #3602, #3629

Fix latest build error in MSVC platform (was broken during development of 3.11.0). #3630

:zap: Improvements

Allow default values for NLOHMANN_DEFINE_TYPE_INTRUSIVE and NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE. #2819, #3143

Avoid clash with Arduino defines. #3338

Improve meta output for MSVC. #3417

Check and warn if a different version of the library is already included (see JSON_SKIP_LIBRARY_VERSION_CHECK). #3418

Re-template json_pointer on string type. #3415

Allow to create booleans from std::vector<bool>::reference. #3533, #3534

Allow to use array types where iterators are pointers. #3544

Improve performance of writing binary formats to byte vectors. #3569

Add patch_inplace function to apply patches without copying. #3581, #3596

Use swap by ADL to allow swapping with non-std containers and improve error messages. #3609

Add versioned, ABI-tagged inline namespace (see NLOHMANN_JSON_NAMESPACE) to avoid ODR errors when linking different versions of the library. #1539, #3360, #3588, #3590

Move UDLs out of the global namespace (see JSON_USE_GLOBAL_UDLS) to avoid name clashes. #1682, #3605

Warnings

Fix ICPC warning 1098. #3632, #3634

Fix a -Wpragmas warning in GCC <11. #3550

:hammer: Further Changes

Fix _MSC_VER version to check for std::filesystem. #3240

Remove <sstream> dependency. #3239, #3244

Overwork bug template to systematically request information. #3348

Add script to test local version in Compiler Explorer. #3456

Change the default value of the CMake parameter JSON_MultipleHeader to ON to always use the multi-header version unless specified otherwise. #3532

Add option to disable default enum conversions (see JSON_DISABLE_ENUM_SERIALIZATION). #3536

Add maintainer targets to create source archive json.tar.xz which can be used in FetchContent. #3289, #3255

Fix CITATION.cff. #3320

Use The Pitchfork Layout (PFL). #3462

Update Cpplint. #3454

More intermediate folders from Visual Studio Code are added to .gitignore. #3572

Add badge for https://repology.org/project/nlohmann-json/versions. #3586

Use REUSE licensing framework. #3546 , #3633, #3635

Install .pc and .cmake files to share directory. #3619

CI

Add support for Visual Studio 2022., #3295

Adjust GitHub Actions CI wrt. windows-latest image. #3368

Remove deprecated windows-2016 image. #3416

Speed up AppVeyor CI. #3422

Update CI image to check with ICPC, GCC 11 and Clang 14. #3420

Add build step for ICPC to CI. #3465

Add more Xcode versions (13.3.1, 13.3, 13.2.1, 13.2, and 13.1) to the CI. #3485

Fix "JSON_MultipleHeaders" option spelling in CI. #3555

Increase timeout for Unicode tests. #3579, #3580, #3614

Abort CI runs on newer commits on the same branch. #3610

Fix MinGW CI failures. #3618

Disable exceptions on ICPC (for the disabled_exceptions unit test). #3621

Unit tests

Improve unit tests. #3380, #3393, #3365, #3405, #3377, #3421, #3422

Disable regression test on GCC <8.4. #3451

Add tests for 32 bit. #3524, #3529, #3530, #3532

Add error message if test suite cannot be found. #3584, #3585

Add unit test to make sure iterator_input_adapter advances iterators correctly. #3548

Add a unit test including <windows.h>. #3631

Documentation and examples

Add more examples to documentation. #3464

Improve documentation on supported types of parse and accept. #3245, #3246

Add documentation on how to parse JSON Lines input. #3247

Fix typos. #3249, #3265, #3426, #3439, #3481, #3499

Document parsing to ordered_json. #3325, #3326

Use FetchContent_MakeAvailable in examples. #3345, #3351

Document requirement of using the same definition of JSON_DIAGNOSTICS in all linked objects. #3360, #3378

Document fuzz testing. #3477, #3478

Add documentation of macros and runtime assertions. #3444, #3431

Fix documentation of JSON Pointer. #3511, #3520

Make certain usage patterns more prominent in the README. #3557

Document precondition for parsing from FILE * and add assertion. #3593

Improve documentation. #3592

Add documentation for comparing json and ordered_json. #3443, #3599

Adjust JSON Pointer examples and add CI step for the examples. #3622

Overwork documentation and add more examples. #3553

:fire: Deprecated functions

The implicit conversion from JSON Pointers to string (json_pointer::operator string_t) has been deprecated. Use json_pointer::to_string instead.

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

The function iterator_wrapper is deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(284.37 KB)
include.zip.asc(833 bytes)
json.hpp(875.47 KB)
json.hpp.asc(833 bytes)
json.tar.xz(105.85 KB)
json.tar.xz.asc(833 bytes)
v3.10.5(Jan 3, 2022)
Release date: 2022-01-03 SHA-256: e832d339d9e0c042e7dff807754769d778cf5d6ae9730ce21eed56de99cb5e86 (json.hpp), b94997df68856753b72f0d7a3703b7d484d4745c567f3584ef97c96c25a5798e (include.zip)

Summary

The previous version 3.10.4 introduced support to convert std::filesystem objects to JSON and vice versa. Unfortunately, we made the assumption that any compiler supporting C++17 would also have proper filesystem support. This was a mistake. This release introduces preprocessor checks (and means to override them) to make sure that the conversion support is only compiled if the compiler is detected to support it.

All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug fixes

Make sure C++17 filesystem conversions are only used if the compiler supports it. Furthermore, add defines JSON_HAS_FILESYSTEM and JSON_HAS_EXPERIMENTAL_FILESYSTEM which can be set to 0 to avoid using filesystem support altogether.std::filesystem. #3090 #3097 #3101 #3156 #3203

Fix a compilation error with Nvidia CUDA Compiler (NVCC). #3013 #3234

Warnings

Fix a warning for shadowed variables. #3188 #3193

Fix a warning on a pointless comparison. #3227 #2712 #2676 #1390 #755

:zap: Improvements

Add a parameter to the update function to recursively merge objects with common keys. #3006 #3069

Extend std::hash and std::swap to work on any nlohmann::basic_json specializations rather than just nlohmann::json. #3121

:hammer: Further Changes

Tests and CI

Update CI to use Clang 14, GCC 6, and Clang-Tidy 14. #3088

Update cpplint. #3225

Add build step for the Nvidia CUDA Compiler (NVCC). #3227

Remove Travis CI. #3087 #3233

Compile and execute the test suite with C++17. #3101

Documentation

The mkdocs-based documentation in doc/mkdocs has been totally overworked. It now has a unified structure, more examples, and contains all information from the previous Doxygen-based documentation. The single source of truth is now the documentation on https://json.nlohmann.me and in particular the API Documentation. #3071

Removed Wandbox online examples. #3071

Fix typos, links, and parameter names in the documentation. #3102 #3125 #3140 #3145 #3148

Add more examples. #3071 #3100

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(254.56 KB)
include.zip.asc(833 bytes)
json.hpp(785.27 KB)
json.hpp.asc(833 bytes)
json.tar.xz(97.50 KB)
v3.10.4(Oct 16, 2021)
Release date: 2021-10-16 SHA-256: c9ac7589260f36ea7016d4d51a6c95809803298c7caec9f55830a0214c5f9140 (json.hpp), 62c585468054e2d8e7c2759c0d990fd339d13be988577699366fe195162d16cb (include.zip)

Summary

This release fixes two bugs introduced in release 3.10.0 and fixes the conversion of std::filesystem::path. All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug Fixes

Fix regression bug introduced in release 3.10.0 which broke compilation for types with an explicit default constructor with default arguments. #3077 #3079

Fix regression bug introduced in release 3.10.0 which treated the return values of std::find and std::remove as pointers which could break compilation. #3081 #3082

Fix converting std::filesystem::path to JSON. Before release 3.10.3, such a conversion would trigger a stack overflow. Release 3.10.3 then further broke compilation on Windows. #3070 #3073

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(322.21 KB)
include.zip.asc(833 bytes)
json.hpp(959.85 KB)
json.hpp.asc(833 bytes)
json.tar.xz(123.38 KB)
v3.10.3(Oct 8, 2021)
Release date: 2021-10-08 SHA-256: bac28658a4c9410faa55960a70c1ac541e8a51bbaae57dc395e23ca5abd3159a (json.hpp), 4ae5744bc1edd216c79f619fd49915c0e490e41b05434c2d2b89e078299f04ed (include.zip)

Summary

This release fixes two more bug introduced in release 3.10.0: the extended diagnostics triggered assertions when used with update() or when inserting elements into arrays. All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug Fixes

Fix bug in the update() function when used with extended diagnostics. #3007 #3008

Fix bug when inserting into arrays when using extended diagnostics. #2926 #3032 #3037

:zap: Improvements

Binary formats

Custom allocators are now supported when writing binary formats (e.g., CBOR, MessagePack) into a std::vector. #2982 #2989

User-defined type support

Allow conversion from types that do not define an explicit iterator type, but have a begin() and end() function. #3020

Tests and CI

Updated the Docker image used in the CI. #2981 #2986

Corrected the compiler version mentioned in the README file. #3040

Documentation

Add script to generate docset for Dash, Velocity, and Zeal. #2967

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(322.21 KB)
include.zip.asc(833 bytes)
json.hpp(959.44 KB)
json.hpp.asc(833 bytes)
json.tar.xz(123.30 KB)
v3.10.2(Aug 26, 2021)
Release date: 2021-08-26 SHA-256: 059743e48b37e41579ee3a92e82e984bfa0d2a9a2b20b175d04db8089f46f047 (json.hpp), 61e605be15e88deeac4582aaf01c09d616f8302edde7adcaba9261ddc3b4ceca (include.zip)

Summary

This release is made days after the 3.10.1 release due to a bug in the release script: The 3.10.1 release at GitHub contained the correct files, but the associated tag v3.10.1 points to the wrong commit. This release is made with a fixed build script. All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:zap: Improvements

Fix the release scripts to correctly tag releases. #2973

Fix some -Wunused warnings on JSON_DIAGNOSTICS when the library is built without CMake. #2975 #2976

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(320.15 KB)
include.zip.asc(833 bytes)
json.hpp(955.59 KB)
json.hpp.asc(833 bytes)
json.tar.xz(122.59 KB)
v3.10.1(Aug 24, 2021)
Release date: 2021-08-24 SHA-256: 0b628af78a2f0f3e2ff41d8dfa18314dd53831ffc2720c2944192d9f53727f4d (json.hpp), 144268f7f85afb0f0fbea7c796723c849724c975f9108ffdadde9ecedaa5f0b1 (include.zip)

Summary

This release fixes a bug introduced in release 3.10.0: the extended diagnostics triggered an assertion when used with ordered_json. All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug Fixes

Fix an assertion triggered in the extended diagnostics using ordered_json. #2962 #2963

Make GDB pretty-printer robust against unset variable names. #2950

:zap: Improvements

Warnings

Add a missing header to hash.hpp. #2948

Fix some -Wextra-semi-stmt warnings. #2957

Tests and CI

Avoid duplicate builds in AppVeyor. #2952

Remove an outdated test binary that is not supported any longer. #2941 #2945

Skip tests that would fail if CMake option JSON_Install is set to OFF. #2946 #2947

Move Travis jobs to travis-ci.com. #2938 #2959

Set stack size for some unit tests when building with MSVC. #2955 #2961

Add a regression test. #2960

Documentation

Update the Homebrew command as nlohmann-json is now in homebrew-core. #2943 #2966

Add example for integration via vcpkg. #2944 #2954

Fix a typo in the documentation. #2968

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(320.12 KB)
include.zip.asc(833 bytes)
json.hpp(955.53 KB)
json.hpp.asc(833 bytes)
json.tar.xz(122.68 KB)
v3.10.0(Aug 17, 2021)
Release date: 2021-08-17 SHA-256: 230f3a03cefd586661ebab577a347c973d97a770afb89e22c52abc3c2a19d0a7 (json.hpp), b5e3bfad07feba218a26a4f809fbb0d1e33450524bf5d7244cabc92cf8178c69 (include.zip)

Summary

JSON for Modern C++ 3.10.0 is the first release for over a year. It contains some new features and a lot of minor changes and bug fixes.

Most notably, it introduces extended diagnostics. By defining JSON_DIAGNOSTICS before including the json.hpp, a JSON Pointer is added to exceptions which helps to debug issues with object access, array indices, or mismatching types.

Another important change behind the curtains is a fully overworked CI which performs a lot of checks for every commit which should allow more frequent releases in the future.

All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:sparkles: New Features

Add extended diagnostics information by adding a JSON Pointer to the exception messages indicating the exact location of a invalid type errors or out-of-bound errors.

[json.exception.type_error.302] (/address/housenumber) type must be number, but is string

Exceptions in the library are thrown in the local context of the JSON value they are detected. This makes detailed diagnostics messages, and hence debugging, difficult. To create better diagnostics messages, each JSON value needs a pointer to its parent value such that a global context (i.e., a path from the root value to the value that lead to the exception) can be created. That global context is then provided as a JSON Pointer.

As this global context comes at the price of storing one additional pointer per JSON value and runtime overhead to maintain the parent relation, extended diagnostics are disabled by default. They can, however, be enabled by defining the preprocessor symbol JSON_DIAGNOSTICS to 1 before including json.hpp. See the documentation for more information. #932 #1508 #2562 #2838 #2866

Add a GDB pretty printer to facilitate reading basic_json values in GDB. #1952 #2607

Add a new value store to the cbor_tag_handler_t which allows to store the tags of CBOR values as binary subtypes. #2863 #2908

Add support for containers with non-default-constructible types. #2574 #2576

:bug: Bug Fixes

Fix a regression bug that failed ordered_json to be used when exceptions were switched off. #2347 #2725 #2934

Added iterator range insertion for ordered_json. #2490 #2512

Change the type of binary subtypes to std::uint64_t to support subtypes >255. Furthermore, the return value of the subtype() function has been fixed to the documented value -1 in case no subtype is given. #2863 #2908

Fix move constructor of internal json_ref type which created null values when compiled with -fno-elide-constructors. #2387 #2405

Fix the compilation of input_adapter for containers in edge cases. #2553

Allow parsing from std::byte containers. #2413 #2546 #2550 #2602 #2869

Fix memory leak in to_json in case a JSON value is reused. #2865 #2872

Fix compilation error in case symbol EOF was not found. #2755 #2756

Fix Compilation error when using NLOHMANN_JSON_SERIALIZE_ENUM with ordered_json on libc++. #2491 #2825

Warnings

A lot of warnings have been fixed in this release. To make sure the library remains warning-free, the CI now breaks in case a warning is found in GCC (261 warning flags), Clang (flag -Weverything with 8 exceptions), or MSVC (flag /W4).

Fix -Wimplicit-fallthrough warnings. #2348 #2349

Fix -Wfloat-equal warnings. #2909 #2911

Add assertions to suppress C28020 warnings. #2447

Fix shadow warnings. #1759 #2536 #2444

Fix compiler warnings in the test suite. #2537

Fix issues found by Visual Studio Visual Assist #2615

Fix unused parameter warning. #2646 #2658 #2668 #2706 #2707

Remove HEDLEY annotation from exception::what() to fix C28204 warning. #2673 #2680

Suppress C4127 warning. #2592 #2875

Fix truncation warning. #2572 #2874

Fix useless cast warning. #1777 #2114 #2893 #2902

Fix unknown pragma warning. #2924 #2925

Fix -Wswitch-enum warnings. #2927

Fix C4309 and C4100 warnings and treat all MSVC /W4 warnings as error. #2930

Suppress fewer warning flags. #2936

:zap: Improvements

Tests and CI

The CI chain has been completely overworked and now runs mostly on a dedicated Docker Image that contains all relevant tools.

Collected all CI calls in a CMake file which can be enabled by setting JSON_CI.

Linux now builds with Clang 3.5 to 12 and GCC 4.8 to 11 checking multiple C++ standards. #2540

Windows builds with MSVC 2015 to 2019, MinGW (GCC 8), Clang 11 and 12, and Clang-CL 11 checking multiple C++ standards.

Mac builds with Xcode 10.2.1 to Xcode 12.4 checking multiple C++ standards. #1798 #2561 #2737 #2790 #2817

Use static analysis tools Clang-Tidy, Cppcheck, Valgrind, Google Sanitizers, Clang Static Analyzer, Cpplint, and Facebook Infer.

Add internal checks for CMake flags, switched off exceptions, header amalgamation, self-contained headers, and exclusion of certain tests via CTest.

Providers: Move most Travis/AppVeyor builds to GitHub Actions. Use Drone CI for aarch64 build. Remove FOSSA. Properly select "Release" build for Travis CI builds. #2375 #2689

Remove #define private public hack from test files. Instead, macro JSON_PRIVATE_UNLESS_TESTED is used in the source code which defaults to private, but can be set to public to test internals. #43 #913 #1985 #2352

CMake

Fixed issue in CMake file that overwrote CMAKE_CXX_COMPILER when the test suite was compiled. #2344 #2384

Only enable CMake options JSON_BuildTests and JSON_Install by default when the library is the main project. #2513 #2514

Add CTest label not_reproducible to skip non-reproducible tests. #2324 #2560

Formatted CMake files ##2770

Add a CMake option JSON_SystemInclude to use SYSTEM in target_include_directories. #2762

Add CMake option JSON_FastTests (OFF by default) to which slow test suite.

Documentation

Fixed typos in the documentation. #2354 #2754

Extended documentation for discarded values and is_discarded() function. #2360 #2363

Fix Markdown of README. #2582

Fix example in README file. #2625 #2659

Fix example in parse exceptions documentation. #2679

Overworked documentation of number handling. #2747

Add link to Conan Center package to README. #2771

Added example for CPM.cmake. #2406

Update README to use HTTPS everywhere. #2789

Fixed consistency of using declarations in README. #2826

Fix documentation of tests that required a Git checkout. #2845

Fix code samples in GIF slideshow. #2457

Update documentation to reference RFC 8259 as JSON standard.

Add section on how to get support to README file.

Replaced links to Doxygen documentation with new API documentation.

Documented the effect of a bug in Microsoft's STL that makes what() member function of exception objects unusable in case _HAS_EXCEPTIONS=0 is set. #2824

Thirdparty

Updated Hedley to version 15. #2367

Updated Doctest to version 2.4.6. #2525 #2538 #2686 #2687

:hammer: Further Changes

Use C++14 constructs where available. #2533

Fix pkg-config.pc generation. #2690

Add possibility to set the C++ standard via macros JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, and JSON_HAS_CPP_20. By defining any of these symbols, the internal check is overridden and the provided C++ version is unconditionally assumed. This can be helpful for compilers that only implement parts of the standard and would be detected incorrectly. #2730 #2731 #2749

Add preprocessor symbol JSON_NO_IO. When defined, headers <cstdio>, <ios>, <iosfwd>, <istream>, and <ostream> are not included and parse functions relying on these headers are excluded. This is relevant for environment where these I/O functions are disallowed for security reasons (e.g., Intel Software Guard Extensions (SGX)). #2728 #2729 #2842 #2861

Benchmarks are handled via FetchContent and require CMake version 3.11. Removed Google Benchmark copy. Fix default branch name for Google Benchmarks. #2795 #2796

Simplify object parser for CBOR. #2879 #2598

Cleaned up maintainer Makefiles

Licensing

Clarified license of is_complete_type implementation. #2534

License fix for integer_sequence and index_sequence implementation. #2683

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(319.42 KB)
include.zip.asc(833 bytes)
json.hpp(954.45 KB)
json.hpp.asc(833 bytes)
json.tar.xz(122.31 KB)
v3.9.1(Aug 6, 2020)
Release date: 2020-08-06 SHA-256: 7804b38146921d03374549c9e2a5e3acda097814c43caf2b96a0278e58df26e0 (json.hpp), 6bea5877b1541d353bd77bdfbdb2696333ae5ed8f9e8cc22df657192218cad91 (include.zip)

Summary

This release fixes two bugs in the features introduced in release 3.9.0. The lexer did not accept consecutive comments, and ordered_json lacked some functions from json. All changes are backward-compatible.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:bug: Bug Fixes

The lexer did not accept input with two or more consecutive comments (e.g. /* one */ /* two */ []). #2330 #2332

The newly introduced ordered_json container did not implement the complete interface of basic_json which broke existing code when json was replaced by ordered_json, in particular when trying to call ordered_json::parse. #2315 #2319 #2331

:hammer: Further Changes

Install pkg-config file to CMAKE_CURRENT_BINARY_DIR instead of CMAKE_BINARY_DIR #2318

Make installation directory of pkg-config file depend on CMAKE_INSTALL_LIBDIR. #2314

Fix -Wimplicit-fallthrough warning. #2333

Fix name of Homebrew formula in documentation. #2326 #2327

Fix typo in documentation. #2320

:fire: Deprecated functions

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(302.06 KB)
include.zip.asc(833 bytes)
json.hpp(904.52 KB)
json.hpp.asc(833 bytes)
v3.9.0(Jul 27, 2020)
Release date: 2020-07-27 SHA-256: d8089d52d285ef2c5368eb39ae665b39ea464206b1ca674a88a915c0245ff4f0 (json.hpp), 5b9b819aed31626aefe2eace23498cafafc1691890556cd36d2a8002f6905009 (include.zip)

JSON for Modern C++ 3.9.0 is a feature release that adds four long-awaited features, some requested five years ago.

The parser functions have now an option to ignore // and /* */ style comments. Though comments are not officially part of the JSON specification (see here for a discussion), comment support was a frequently requested feature, and its implementation was much less effort than continuously explaining the lack of comment support.

The second-most requested feature was a way to preserve the insertion order of object keys. Though this was possible via template specialization for a while, we now added a new type nlohmann::ordered_json as drop-in replacement for nlohmann::json for this.

To circumvent unexpected behavior, implicit conversions can now be switched off with a CMake or preprocessor option.

Last, but not least, a mapping between user-defined types and JSON can now be expressed using convenience macros by just listing the names of the member variables to read/write.

All changes are backward-compatible. See below the complete list of changes. See the README or the documentation for more information.

:moneybag: Note you can support this project via GitHub sponsors or PayPal.

:sparkles: New Features

Add optional support for comments in JSON: passing parameter ignore_comments to the parse function will treat // and /* */ comments like whitespace. #294 #363 #376 #597 #1513 #2061 #2212

Add type nlohmann::ordered_json to preserve insertion order of object keys. ordered_json is a specialization of basic_json and can be used wherever json is used. #106 #424 #543 #660 #727 #952 #1106 #1717 #1817 #2179 #2206 #2258

Add CMake option JSON_ImplicitConversions and preprocessor symbol JSON_USE_IMPLICIT_CONVERSIONS to switch off implicit conversions. Implicit conversions, though very practical, are also a source of subtle bugs or unexpected behavior and may be switched off by default in future versions. The new options allow to remove implicit conversions now. #958 #1559

Add convenience macros NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE and NLOHMANN_DEFINE_TYPE_INTRUSIVE to simplify serialization/deserialization code for user-defined types. #2175 #2225 #2233 #2267 #2280 #2287 #2306 #2313

Add high-precision number support for UBJSON. Now, any JSON value can serialized to UBJSON, and exception json.exception.out_of_range.407 will no longer occur for integers larger than 9223372036854775807 (LLONG_MAX). #2297 #2286

Write binary subtype as CBOR tag. #2244

Add option to ignore CBOR tags as alternative to treat them as invalid input. #2308 #2273 #1968

:bug: Bug Fixes

Fix bug in CBOR parser where allow_exceptions was not respected. #2299 #2298

Fix bug in CBOR parser where incomplete binary values or strings could crash the parser. #2293 #2294

:zap: Improvements

Make code compile with Clang on Windows. #2259 #1119

Use 32-bit float encoding in MessagePack wherever this is possible without loss of precision. #2201 #2196

Replace std::hash<nlohmann::basic_json> with a function that does not allocate memory. #2292 #2285 #2269

:hammer: Further Changes

Use GitLab Discussions for support and feature requests. Removed and adjusted issue templates accordingly.

Allow CMake 3.13+ to override options when using FetchContent. #2222

Add support for pkg-config. #2253

Add CMake option JSON_TestDataDirectory to select directory of previously downloaded test data for situations where Internet access is forbidden during testing. #2189 #2190

Add option to skip tests that assume the code is checked out via Git. #2189

Add JSON_ASSERT macro to control behavior of assert calls. #2242

Add CI step for GitHub CodeQL analysis (GitHub actions).

Add CI step for Clang 9 and Clang 10 on Windows (GitHub actions). #2259

Add CI step for Clang 10 CL with MSVC 2019 on Windows (GitHub actions). #2268

Clean up GitHub actions CI. #2300

Add CI step for Xcode 12 (Travis). #2262

Add CI step for explicit conversions (Travis, AppVeyor).

Remove swap specialization to support C++20. #2176

Add missing check for binary() function in SAX interface. #2282

Add test for CMake target_include_directories. #2279

Add test to use library in multiple translation units. #2301

Add more sections to new project website. #2312

Fix warnings. #2304 #2305 #2303 #2274 #2224 #2211 #2203

Cleanup maintainer Makefiles. #2264 #2274

Improve documentation. #2232

Fix inconsistency in int-to-string function. #2193

:fire: Deprecated functions

Passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists is deprecated. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(301.64 KB)
include.zip.asc(833 bytes)
json.hpp(902.26 KB)
json.hpp.asc(833 bytes)
v3.8.0(Jun 14, 2020)
Release date: 2020-06-14 SHA-256: be7bbfbc7c62c35aa6f27dfbdd950384f247dd9f2281b5930bdaa3a6ab95eef7 (json.hpp), 8590fbcc2346a3eefc341935765dd57598022ada1081b425678f0da9a939a3c0 (include.zip)

Summary

It has been six months since the last release, and a lot of minor changes and bug fixes have accumulated. Nonetheless, JSON for Modern C++ 3.8.0 is a feature release.

With binary values we greatly extend the support for binary formats such as CBOR, BSON, or MessagePack. By adding a new value type to the JSON class, binary values can be read and written, and even shared between different formats. See the documentation for examples.

Furthermore, we overworked the input adapters; that is, the way input is read by the parsers. Now any container is supported via the LegacyInputIterator concept. See the documentation for examples. At the same time, we could improve the performance by 3-10%.

All changes are backward-compatible. See below the complete list of changes.

:moneybag: Note you can now support this project via GitHub sponsors or PayPal.

:sparkles: New Features

The library now supports binary values for CBOR (byte arrays), BSON, and MessagePack (bin, ext, fixext). The values are parsed into a byte vector for further processing. #483 #757 #1129 #1509 #1662 #1668 #2064 #2069 #2071 #2082 #2099

The input adapters have been generalized to read from any container including user-defined containers via LegacyInputIterator. The encoding of the input is implicitly derived from the size of the value type: UTF-8 (1 byte), UTF-16 (2 bytes), and UTF-32 (4 bytes) are supported. #1813 #2145 #2174 #2178

CBOR now encodes floating-point numbers that can be represented by a float as float to save space in the serialization (32 bit va. 64 bit). #1719 #2044

:bug: Bug Fixes

The functions to parse binary formats (from_bson, from_cbor, from_msgpack, and from_ubjson) now properly respect the allow_exceptions=false parameter. #1715 #2140

The contains function for JSON Pointers now returns false in all cases a syntactically correct JSON Pointer refers to a non-existing value. Previously, an exception was raised if a JSON Pointer referred to an array, but did not consist of a number. #1942 #1982 #2019

Fixed the JSON Pointer parser which accepted numbers with leading + as array index. #1990

Fixed JSON Patch generation to properly use /- in the add operation for arrays. #1983 #2054

Fixed compilation errors using GCC 10. #1912 #1920 #2034

Fixed compilation errors using MSVC 2019. #1695 #1810 #1958 #2006 #2008 #2009

Fixed a preprocessor check for some MSVC versions. #2112 #2137

Fixed possible memory leak in push_back. #1971 #2025

Removed broken overload of the value() function with json::value_t type parameter. #2086 #2104

Removed values from arrays in case they are discarded by a parser callback function. Such values remained in the array with type discarded before. #1972 #2153

:zap: Improvements

The input adapters are now used via templates rather than inheriting from an abstract base class. This brings a 3-10% speedup for all parsers. #1457 #1950

Test files are now downloaded from an external repository such that the code repository got much smaller and can be used as submodule more easily. #96 #482 #556 #567 #620 #732 #1066 #1184 #1185 #1235 #1497 #1572 #1790 #2081

Made CMake's version config file architecture-independent. #1697 #1746

:hammer: Further Changes

Added links to GitHub sponsors and listed named sponsors.

Documented the integration of the library via CMake FetchContent #2073 #2074

Doozer CI was removed as it seems to exist no longer. #2080

Added GitHub Actions workflows to build with Ubuntu, macOS, and Windows.

Added GCC 10.1 to the continuous integration. #2136

Fixed the Coveralls integration. #2100

Fixed the error message for invalid surrogate pairs. #2076

Fixed documentation. #1853 #1857 #1895 #1903 #1907 #1915 #1917 #1918 #1923 #1956 #1979 #1980 #2002 #2060 #2077 #2142 #2143 #2152

Added test cases for NaN value in CBOR. #2043

Documented curious behavior when using the library with glibc. #1924 #1933

Fixed compiler warnings. #1939 #1911 #1967 #1969 #2049 #2051 #2053 #2113 #2116 #2144 #2177

Updated Doctest to version 2.3.7. #2048 #2050

Updated Hedley to version 13.

Removed std::is_pod usage as it is deprecated in C++20. #1913 #2033 #2109

Added wsjcpp package manager. #2004

Added Build2 package manager. #1909

Fixed compiler warning in test case. #1871

Updated copyright year. #2010

Updated CMake tests. #1844

Removed a duplicated test. #2158

Removed outdated Travis macOS images for Xcode 8.3, Xcode 9.0, Xcode 9.1, and Xcode 9.2. Added Xcode 11.2 image.

Added FOSSA analysis.

Header <ciso646> is deprecated in C++17 and not included if library is compiled with C++17. #2089 .#2115

Updated the templates for bug fix reports, feature requests, and questions.

Added fuzz tests for the all UBJSON modes. #2182

Used HEDLEY_DEPRECATED_FOR to indicate deprecated functions to have supporting compilers report which function to use instead.

:fire: Deprecated functions

This release deprecates passing iterator pairs or pointer/length pairs to parsing functions (basic_json::parse, basic_json::accept, basic_json::sax_parse, basic_json::from_cbor, basic_json::from_msgpack, basic_json::from_ubjson, basic_json::from_bson) via initializer lists. Instead, pass two iterators; for instance, call basic_json::from_cbor(ptr, ptr+len) instead of basic_json::from_cbor({ptr, len}).

The following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

All deprecations are annotated with HEDLEY_DEPRECATED_FOR to report which function to use instead.
Source code(tar.gz)
Source code(zip)
include.zip(290.78 KB)
include.zip.asc(833 bytes)
json.hpp(855.72 KB)
json.hpp.asc(833 bytes)
v3.7.3(Nov 17, 2019)
Release date: 2019-11-17 SHA-256: 3b5d2b8f8282b80557091514d8ab97e27f9574336c804ee666fda673a9b59926 (json.hpp), 87b5884741427220d3a33df1363ae0e8b898099fbc59f1c451113f6732891014 (include.zip)

Summary

This release fixes a bug introduced in release 3.7.2 which could yield quadratic complexity in destructor calls. All changes are backward-compatible.

:bug: Bug Fixes

Removed reserve() calls from the destructor which could lead to quadratic complexity. #1837 #1838

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(274.38 KB)
include.zip.asc(833 bytes)
json.hpp(790.51 KB)
json.hpp.asc(833 bytes)
v3.7.2(Nov 10, 2019)
Release date: 2019-11-10 SHA-256: 0a65fcbbe1b334d3f45c9498e5ee28c3f3b2428aea98557da4a3ff12f0f14ad6 (json.hpp), 67f69c9a93b7fa0612dc1b6273119d2c560317333581845f358aaa68bff8f087 (include.zip)

Summary

Project bad_json_parsers tested how JSON parser libraries react on deeply nested inputs. It turns out that this library segfaulted at a certain nesting depth. This bug was fixed with this release. Now the parsing is only bounded by the available memory. All changes are backward-compatible.

:bug: Bug Fixes

Fixed a bug that lead to stack overflow for deeply nested JSON values (objects, array) by changing the implementation of the destructor from a recursive to an iterative approach. #832, #1419, #1835

:hammer: Further Changes

Added WhiteStone Bolt. #1830

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(274.34 KB)
include.zip.asc(833 bytes)
json.hpp(790.55 KB)
json.hpp.asc(833 bytes)
v3.7.1(Nov 6, 2019)
Release date: 2019-11-06 SHA-256: b5ba7228f3c22a882d379e93d08eab4349458ee16fbf45291347994eac7dc7ce (json.hpp), 77b9f54b34e7989e6f402afb516f7ff2830df551c3a36973085e2c7a6b1045fe (include.zip)

Summary

This release fixes several small bugs in the library. All changes are backward-compatible.

:bug: Bug Fixes

Fixed a segmentation fault when serializing std::int64_t minimum value. #1708 #1722

Fixed the contains() function for JSON Pointers. #1727 #1741

Fixed too lax SFINAE guard for conversion from std::pair and std::tuple to json. #1805 #1806 #1825 #1826

Fixed some regressions detected by UBSAN. Updated CI to use Clang-Tidy 7.1.0. #1716 #1728

Fixed integer truncation in iteration_proxy. #1797

Updated Hedley to v11 to fix a E2512 error in MSVC. #1799

Fixed a compile error in enum deserialization of non non-default-constructible types. #1647 #1821

Fixed the conversion from json to std::valarray.

:zap: Improvements

The items() function can now be used with a custom string type. #1765

Made json_pointer::back const. #1764 #1769

Meson is part of the release archive. #1672 #1694

Improved documentation on the Meson and Spack package manager. #1694 #1720

:hammer: Further Changes

Added GitHub Workflow with ubuntu-latest/GCC 7.4.0 as CI step.

Added GCC 9 to Travis CI to compile with C++20 support. #1724

Added MSVC 2019 to the AppVeyor CI. #1780

Added badge to fuzzing status.

Fixed some cppcheck warnings. #1760

Fixed several typos in the documentation. #1720 #1767 #1803

Added documentation on the JSON_THROW_USER, JSON_TRY_USER, and JSON_CATCH_USER macros to control user-defined exception handling.

Used GitHub's CODEOWNERS and SECURITY feature.

Removed GLOB from CMake files. #1779

Updated to Doctest 2.3.5.

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(273.45 KB)
include.zip.asc(833 bytes)
json.hpp(788.83 KB)
json.hpp.asc(833 bytes)
v3.7.0(Jul 28, 2019)
Release date: 2019-07-28 SHA-256: a503214947952b69f0062f572cb74c17582a495767446347ce2e452963fc2ca4 (json.hpp), 541c34438fd54182e9cdc68dd20c898d766713ad6d901fb2c6e28ff1f1e7c10d (include.zip)

Summary

This release introduces a few convenience functions and performs a lot of house keeping (bug fixes and small improvements). All changes are backward-compatible.

:sparkles: New Features

Add overload of the contains function to check if a JSON pointer is valid without throwing exceptions, just like its counterpart for object keys. #1600

Add a function to_string to allow for generic conversion to strings. #916 #1585

Add return value for the emplace_back function, returning a reference to the added element just like C++17 is introducing this for std::vector. #1609

Add info how to use the library with the pacman package manager on MSYS2. #1670

:bug: Bug Fixes

Fix an issue where typedefs with certain names yielded a compilation error. #1642 #1643

Fix a conversion to std::string_view in the unit tests. #1634 #1639

Fix MSVC Debug build. #1536 #1570 #1608

Fix get_to method to clear existing content before writing. #1511 #1555

Fix a -Wc++17-extensions warning. nodiscard attributes are now only used with Clang when -std=c++17 is used. #1535 #1551

:zap: Improvements

Switch from Catch to doctest for the unit tests which speeds up compilation and runtime of the 112,112,308 tests.

Add an explicit section to the README about the frequently addressed topics character encoding, comments in JSON, and the order of object keys.

:hammer: Further Changes

Use GNUInstallDirs to set library install directories. #1673

Fix links in the README. #1620 #1621 #1622 #1623 #1625

Mention json type on the documentation start page. #1616

Complete documentation of value() function with respect to type_error.302 exception. #1601

Fix links in the documentation. #1598

Add regression tests for MSVC. #1543 #1570

Use CircleCI for continuous integration.

Use Doozer for continuous integration on Linux (CentOS, Raspbian, Fedora)

Add tests to check each CMake flag (JSON_BuildTests, JSON_Install, JSON_MultipleHeaders, JSON_Sanitizer, JSON_Valgrind, JSON_NoExceptions, JSON_Coverage).

Use Hedley to avoid re-inventing several compiler-agnostic feature macros like JSON_DEPRECATED, JSON_NODISCARD, JSON_LIKELY, JSON_UNLIKELY, JSON_HAS_CPP_14, or JSON_HAS_CPP_17. Functions taking or returning pointers are annotated accordingly when a pointer will not be null.

Build and run tests on AppVeyor in DEBUG and RELEASE mode.

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(142.63 KB)
include.zip.asc(833 bytes)
json.hpp(782.23 KB)
json.hpp.asc(833 bytes)
v3.6.1(Mar 20, 2019)
Release date: 2019-03-20 SHA-256: d2eeb25d2e95bffeb08ebb7704cdffd2e8fca7113eba9a0b38d60a5c391ea09a (json.hpp), 69cc88207ce91347ea530b227ff0776db82dcb8de6704e1a3d74f4841bc651cf (include.zip)

Summary

This release fixes a regression and a bug introduced by the earlier 3.6.0 release. All changes are backward-compatible.

:bug: Bug Fixes

Fixed regression of #590 which could lead to compilation errors with GCC 7 and GCC 8. #1530

Fixed a compilation error when <Windows.h> was included. #1531

:hammer: Further Changes

Fixed a warning for missing field initializers. #1527

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(135.95 KB)
include.zip.asc(833 bytes)
json.hpp(711.28 KB)
json.hpp.asc(833 bytes)
v3.6.0(Mar 19, 2019)
Release date: 2019-03-20 SHA-256: ce9839370f28094c71107c405affb3b08c4a098154988014cbb0800b1c44a831 (json.hpp), 237c5e66e7f8186a02804ce9dbd5f69ce89fe7424ef84adf6142e973bd9532f4 (include.zip)

ℹ️ This release introduced a regression. Please update to version 3.6.1!

Summary

This release adds some convenience functions for JSON Pointers, introduces a contains function to check if a key is present in an object, and improves the performance of integer serialization. Furthermore, a lot of small bug fixes and improvements have been made. All changes are backward-compatible.

:sparkles: New Features

Overworked the public interface for JSON Pointers. The creation of JSON Pointers is simplified with operator/ and operator/=. JSON Pointers can be inspected with empty, back, and parent_pointer, and manipulated with push_back and pop_back. #1434

Added a boolean method contains to check whether an element exists in a JSON object with a given key. Returns false when called on non-object types. #1471 #1474

:bug: Bug Fixes

Fixed a compilation issues with libc 2.12. #1483 #1514

Fixed endian conversion on PPC64. #1489

Fixed library to compile with GCC 9. #1472 #1492

Fixed a compilation issue with GCC 7 on CentOS. #1496

Fixed an integer overflow. #1447

Fixed buffer flushing in serializer. #1445 #1446

:zap: Improvements

The performance of dumping integers has been greatly improved. #1411

Added CMake parameter JSON_Install to control whether the library should be installed (default: on). #1330

Fixed a lot of compiler and linter warnings. #1400 #1435 #1502

Reduced required CMake version from 3.8 to 3.1. #1409 #1428 #1441 #1498

Added nodiscard attribute to meta(), array(), object(), from_cbor, from_msgpack, from_ubjson, from_bson, and parse. #1433

:hammer: Further Changes

Added missing headers. #1500

Fixed typos and broken links in README. #1417 #1423 #1425 #1451 #1455 #1491

Fixed documentation of parse function. #1473

Suppressed warning that cannot be fixed inside the library. #1401 #1468

Imroved package manager suppert:

Updated Buckaroo instructions. #1495

Improved Meson support. #1463

Added Conda package manager documentation. #1430

Added NuGet package manager documentation. #1132

Continuous Integration

Removed unstable or deprecated Travis builders (Xcode 6.4 - 8.2) and added Xcode 10.1 builder.

Added Clang 7 to Travis CI.

Fixed AppVeyor x64 builds. #1374 #1414

Updated thirdparty libraries:

Catch 1.12.0 -> 1.12.2

Google Benchmark 1.3.0 -> 1.4.1

Doxygen 1.8.15 -> 1.8.16

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(135.90 KB)
include.zip.asc(833 bytes)
json.hpp(711.14 KB)
json.hpp.asc(833 bytes)
v3.5.0(Dec 21, 2018)
Release date: 2018-12-22 SHA-256: 8a6dbf3bf01156f438d0ca7e78c2971bca50eec4ca6f0cf59adf3464c43bb9d5 (json.hpp), 3564da9c5b0cf2e032f97c69baedf10ddbc98030c337d0327a215ea72259ea21 (include.zip)

Summary

This release introduces the support for structured bindings and reading from FILE*. Besides, a few bugs have been fixed. All changes are backward-compatible.

:sparkles: New Features

Structured bindings are now supported for JSON objects and arrays via the items() member function, so finally this code is possible:

for (auto& [key, val] : j.items()) { std::cout << key << ':' << val << '\n'; }

#1388 #1391

Added support for reading from FILE* to support situations in which streams are nit available or would require too much RAM. #1370 #1392

:bug: Bug Fixes

The eofbit was not set for input streams when the end of a stream was reached while parsing. #1340 #1343

Fixed a bug in the SAX parser for BSON arrays.

:zap: Improvements

Added support for Clang 5.0.1 (PS4 version). #1341 #1342

:hammer: Further Changes

Added a warning for implicit conversions to the documentation: It is not recommended to use implicit conversions when reading from a JSON value. Details about this recommendation can be found here. #1363

Fixed typos in the documentation. #1329 #1380 #1382

Fixed a C4800 warning. #1364

Fixed a -Wshadow warning #1346

Wrapped std::snprintf calls to avoid error in MSVC. #1337

Added code to allow installation via Meson. #1345

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(133.28 KB)
include.zip.asc(833 bytes)
json.hpp(693.35 KB)
json.hpp.asc(833 bytes)
v3.4.0(Oct 30, 2018)
Release date: 2018-10-30 SHA-256: 63da6d1f22b2a7bb9e4ff7d6b255cf691a161ff49532dcc45d398a53e295835f (json.hpp), bfec46fc0cee01c509cf064d2254517e7fa80d1e7647fea37cf81d97c5682bdc (include.zip)

Summary

This release introduces three new features:

BSON (Binary JSON) is next to CBOR, MessagePack, and UBJSON the fourth binary (de)serialization format supported by the library.

Adjustable error handlers for invalid Unicode allows to specify the behavior when invalid byte sequences are serialized.

Simplified enum/JSON mapping with a macro in case the default mapping to integers is not desired.

Furthermore, some effort has been invested in improving the parse error messages. Besides, a few bugs have been fixed. All changes are backward-compatible.

:sparkles: New Features

The library can read and write a subset of BSON (Binary JSON). All data types known from JSON are supported, whereas other types more tied to MongoDB such as timestamps, object ids, or binary data are currently not implemented. See the README for examples. #1244 #1320

The behavior when the library encounters an invalid Unicode sequence during serialization can now be controlled by defining one of three Unicode error handlers: (1) throw an exception (default behavior), (2) replace invalid sequences by the Unicode replacement character (U+FFFD), or (3) ignore/filter invalid sequences. See the documentation of the dump function for examples. #1198 #1314

To easily specify a user-defined enum/JSON mapping, a macro NLOHMANN_JSON_SERIALIZE_ENUM has been introduced. See the README section for more information. #1208 #1323

:bug: Bug Fixes

fixed truncation #1286 #1315

fixed an issue with std::pair #1299 #1301

fixed an issue with std::variant #1292 #1294

fixed a bug in the JSON Pointer parser

:zap: Improvements

The diagnosis messages for parse errors have been improved: error messages now indicated line/column positions where possible (in addition to a byte count) and also the context in which the error occurred (e.g., "while parsing a JSON string"). Example: error parse error at 2: syntax error - invalid string: control character must be escaped; last read: '<U+0009>' is now reported as parse error at line 1, column 2: syntax error while parsing value - invalid string: control character U+0009 (HT) must be escaped to \u0009 or \t; last read: '<U+0009>'. #1280 #1288 #1303

:hammer: Further Changes

improved Meson documentation #1305

fixed some more linter warnings #1280

fixed Clang detection for third-party Google Benchmark library #1277

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(131.92 KB)
include.zip.asc(833 bytes)
json.hpp(689.37 KB)
json.hpp.asc(833 bytes)
v3.3.0(Oct 5, 2018)
Release date: 2018-10-05 SHA-256: f1327bb60c58757a3dd2b0c9c45d49503d571337681d950ec621f8374bcc14d4 (json.hpp), 9588d63557333aaa485e92221ec38014a85a6134e7486fe3441e0541a5a89576 (include.zip)

Summary

This release adds support for GCC 4.8. Furthermore, it adds a function get_to to write a JSON value to a passed reference. Another topic of this release was the CMake support which has been overworked and documented.

Besides, a lot of bugs have been fixed and slight improvements have been made. All changes are backward-compatible.

:sparkles: New Features

The library can now also built with GCC 4.8. Though this compiler does not fully support C++11, it can successfully compile and run the test suite. Note that bug 57824 in GCC 4.8 still forbids to use multiline raw strings in arguments to macros. #1257

Added new function get_to to write a JSON value to a passed reference. The destination type is automatically derived which allows more succinct code compared to the get function. #1227 #1231

:bug: Bug Fixes

Fixed a bug in the CMake file that made target_link_libraries to not properly include nlohmann_json. #1243 #1245 #1260

Fixed a warning in MSVC 2017 complaining about a constexpr if. #1204 #1268 #1272

Fixed a bug that prevented compilation with ICPC. #755 #1222

Improved the SFINAE correctness to fix a bug in the conversion operator. #1237 #1238

Fixed a -Wctor-dtor-privacy warning. #1224

Fixed a warning on a lambda in unevaluated context. #1225 #1230

Fixed a bug introduced in version 3.2.0 where defining JSON_CATCH_USER led to duplicate macro definition of JSON_INTERNAL_CATCH. #1213 #1214

Fixed a bug that prevented compilation with Clang 3.4.2 in RHEL 7. #1179 #1249

:zap: Improvements

Added documentation on CMake integration of the library. #1270

Changed the CMake file to use find_package(nlohmann_json) without installing the library. #1202

Improved error messages in case operator[] is used with the wrong combination (json.exception.type_error.305) of JSON container type and argument type. Example: "cannot use operator[] with a string argument". #1220 #1221

Added a license and version information to the Meson build file. #1252

Removed static assertions to indicated missing to_json or from_json functions as such assertions do not play well with SFINAE. These assertions also led to problems with GMock. #960 #1212 #1228

The test suite now does not wait forever if run in a wrong directory and input files are not found. #1262

The test suite does not show deprecation warnings for deprecated functions which frequently led to confusion. #1271

:hammer: Further Changes

GCC 4.8 and Xcode 10 were added to the continuous integration suite at Travis.

Added lgtm checks to pull requests.

Added tests for CMake integration. #1260

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(123.26 KB)
include.zip.asc(833 bytes)
json.hpp(635.41 KB)
json.hpp.asc(833 bytes)
v3.2.0(Aug 20, 2018)
Release date: 2018-08-20 SHA-256: ce6b5610a051ec6795fa11c33854abebb086f0fd67c311f5921c3c07f9531b44 (json.hpp), 35ee642558b90e2f9bc758995c4788c4b4d4dec54eef95fb8f38cb4d49c8fc7c (include.zip)

Summary

This release introduces a SAX interface to the library. While this may be a very special feature used by only few people, it allowed to unify all functions that consumed input and created some kind of JSON value. Internally, now all existing functions like parse, accept, from_cbor, from_msgpack, and from_ubjson use the SAX interface with different event processors. This allowed to separate the input processing from the value generation. Furthermore, throwing an exception in case of a parse error is now optional and up to the event processor. Finally, the JSON parser is now non-recursive (meaning it does not use the call stack, but std::vector<bool> to track the hierarchy of structured values) which allows to process nested input more efficiently.

Furthermore, the library finally is able to parse from wide string types. This is the first step toward opening the library from UTF-8 to UTF-16 and UTF-32.

This release further fixes several bugs in the library. All changes are backward-compatible.

:sparkles: New Features

added a parser with a SAX interface (#971, #1153)

support to parse from wide string types std::wstring, std::u16string, and std::u32string; the input will be converted to UTF-8 (#1031)

added support for std::string_view when using C++17 (#1028)

allow to roundtrip std::map and std::unordered_map from JSON if key type is not convertible to string; in these cases, values are serialized to arrays of pairs (#1079, #1089, #1133, #1138)

:bug: Bug Fixes

allow to create nullptr_t from JSON allowing to properly roundtrip null values (#1169)

allow compare user-defined string types (#1130)

better support for algorithms using iterators from items() (#1045, #1134)

added parameter to avoid compilation error with MSVC 2015 debug builds (#1114)

re-added accidentially skipped unit tests (#1176)

fixed MSVC issue with std::swap (#1168)

:zap: Improvements

key() function for iterators returns a const reference rather than a string copy (#1098)

binary formats CBOR, MessagePack, and UBJSON now supports float as type for floating-point numbers (#1021)

:hammer: Further Changes

changed issue templates

improved continuous integration: added builders for Xcode 9.3 and 9.4, added builders for GCC 8 and Clang 6, added builder for MinGW, added builders for MSVC targeting x86

required CMake version is now at least 3.8 (#1040)

overworked CMake file wrt. packaging (#1048)

added package managers: Spack (#1041) and CocoaPods (#1148)

fixed Meson include directory (#1142)

preprocessor macro JSON_SKIP_UNSUPPORTED_COMPILER_CHECK can skip the rejection of unsupported compilers - use at your own risk! (#1128)

preprocessor macro JSON_INTERNAL_CATCH/JSON_INTERNAL_CATCH_USER allows to control the behavior of exception handling inside the library (#1187)

added note on char to JSON conversion

added note how to send security-related issue via encrypted email

removed dependency to std::stringstream (#1117)

added SPDX-License-Identifier

added updated JSON Parsing Test Suite, described in Parsing JSON is a Minefield 💣

updated to Catch 1.12.0

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(123.86 KB)
include.zip.asc(833 bytes)
json.hpp(635.79 KB)
json.hpp.asc(833 bytes)
v3.1.2(Mar 14, 2018)
Release date: 2018-03-14 SHA-256: fbdfec4b4cf63b3b565d09f87e6c3c183bdd45c5be1864d3fcb338f6f02c1733 (json.hpp), 495362ee1b9d03d9526ba9ccf1b4a9c37691abe3a642ddbced13e5778c16660c (include.zip)

Summary

This release fixes several bugs in the library. All changes are backward-compatible.

:bug: Bug Fixes

Fixed a memory leak occurring in the parser callback (#1001).

Different specializations of basic_json (e.g., using different template arguments for strings or objects) can now be used in assignments (#972, #977, #986).

Fixed a logical error in an iterator range check (#992).

:zap: Improvements

The parser and the serialization now support user-defined string types (#1006, #1009).

:hammer: Further Changes

Clang Analyzer is now used as additional static analyzer; see make clang_analyze.

Overworked README by adding links to the documentation (#981).

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(114.85 KB)
include.zip.asc(833 bytes)
json.hpp(581.85 KB)
json.hpp.asc(833 bytes)
v3.1.1(Feb 13, 2018)
Release date: 2018-02-13 SHA-256: e14ce5e33d6a2daf748026bd4947f3d9686ca4cfd53d10c3da46a0a9aceb7f2e (json.hpp), fde771d4b9e4f222965c00758a2bdd627d04fb7b59e09b7f3d1965abdc848505 (include.zip)

Summary

This release fixes several bugs in the library. All changes are backward-compatible.

:bug: Bug Fixes

Fixed parsing of CBOR strings with indefinite length (#961). Earlier versions of this library misinterpreted the CBOR standard and rejected input with the 0x7F start byte.

Fixed user-defined conversion to vector type (#924, #969). A wrong SFINAE check rejected code though a user-defined conversion was provided.

Fixed documentation of the parser behavior for objects with duplicate keys (#963). The exact behavior is not specified by RFC 8259 and the library now also provides no guarantee which object key is stored.

Added check to detect memory overflow when parsing UBJSON containers (#962). The optimized UBJSON format allowed for specifying an array with billions of null elements with a few bytes and the library did not check whether this size exceeded max_size().

:hammer: Further Changes

Code coverage is now calculated for the individual header files, allowing to find uncovered lines more quickly than by browsing through the single header version (#953, #957).

A Makefile target run_benchmarks was added to quickly build and run the benchmark suite.

The documentation was harmonized with respect to the header inclusion (#955). Now all examples and the README use #include <nlohmann/json.hpp> to allow for selecting single_include or include or whatever installation folder as include directory.

Added note on how to use the library with the cget package manager (#954).

:fire: Deprecated functions

This release does not deprecate any functions. As an overview, the following functions have been deprecated in earlier versions and will be removed in the next major version (i.e., 4.0.0):

Function iterator_wrapper are deprecated. Please use the member function items() instead.

Functions friend std::istream& operator<<(basic_json&, std::istream&) and friend std::ostream& operator>>(const basic_json&, std::ostream&) are deprecated. Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

Source code(tar.gz)
Source code(zip)
include.zip(114.18 KB)
include.zip.asc(833 bytes)
json.hpp(577.25 KB)
json.hpp.asc(833 bytes)
v3.1.0(Feb 1, 2018)
Release date: 2018-02-01 SHA-256: d40f614d10a6e4e4e80dca9463da905285f20e93116c36d97d4dc1aa63d10ba4 (json.hpp), 2b7234fca394d1e27b7e017117ed80b7518fafbb4f4c13a7c069624f6f924673 (include.zip)

Summary

This release adds support for the UBJSON format and JSON Merge Patch. It also contains some minor changes and bug fixes. All changes are backward-compatible.

:sparkles: New features

The library now supports UBJSON (Universal Binary JSON Specification) as binary format to read and write JSON values space-efficiently. See the documentation overview for a comparison of the different formats CBOR, MessagePack, and UBJSON.

JSON Merge Patch (RFC 7386) offers an intuitive means to describe patches between JSON values (#876, #877). See the documentation of merge_patch for more information.

:zap: Improvements

The library now uses the Grisu2 algorithm for printing floating-point numbers (based on the reference implementation by Florian Loitsch) which produces a short representation which is guaranteed to round-trip (#360, #935, #936).

The UTF-8 handling was further simplified by using the decoder of Björn Hoehrmann in more scenarios.

:truck: Reorganization

Though the library is released as a single header, its development got more and more complicated. With this release, the header is split into several files and the single-header file json.hpp can be generated from these development sources. In the repository, folder include contains the development sources and single_include contains the single json.hpp header (#700, #906, #907, #910, #911, #915, #920, #924, #925, #928, #944).

The split further allowed for a forward declaration header include/nlohmann/json_fwd.hpp to speed up compilation times (#314).

:hammer: Further changes

Google Benchmark is now used for micro benchmarks (see benchmarks folder, #921).

The serialization (JSON and binary formats) now properly work with the libraries string template parameter, allowing for optimized string implementations to be used in constraint environments such as embedded software (#941, #950).

The exceptional behavior can now be overridden by defining macros JSON_THROW_USER, JSON_TRY_USER, and JSON_CATCH_USER, defining the behavior of throw, try and catch, respectively. This allows to switch off C++'s exception mechanism yet still execute user-defined code in case an error condition occurs (#938).

To facilitate the interplay with flex and Bison, the library does not use the variable name yytext any more as it could clash with macro definitions (#933).

The library now defines NLOHMANN_JSON_VERSION_MAJOR, NLOHMANN_JSON_VERSION_MINOR, and NLOHMANN_JSON_VERSION_PATCH to allow for conditional compilation based on the included library version (#943, #948).

A compilation error with ICC has been fixed (#947).

Typos and links in the documentation have been fixed (#900, #930).

A compiler error related to incomplete types has been fixed (#919).

The tests form the UTF-8 decoder stress test have been added to the test suite.

:fire: Deprecated functions

Function iterator_wrapper has been deprecated (#874). Since its introduction, the name was up for discussion, as it was too technical. We now introduced the member function items() with the same semantics. iterator_wrapper will be removed in the next major version (i.e., 4.0.0).

Furthermore, the following functions are deprecated since version 3.0.0 and will be removed in the next major version (i.e., 4.0.0):

friend std::istream& operator<<(basic_json&, std::istream&)

friend std::ostream& operator>>(const basic_json&, std::ostream&)

Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.
Source code(tar.gz)
Source code(zip)
include.zip(114.00 KB)
include.zip.asc(833 bytes)
json.hpp(576.54 KB)
json.hpp.asc(833 bytes)
v3.0.1(Dec 29, 2017)
Release date: 2017-12-29 SHA-256: c9b3591f1bb94e723a0cd7be861733a3a555b234ef132be1e9027a0364118c4c

Summary

This release fixes small issues in the implementation of JSON Pointer and JSON Patch. All changes are backward-compatible.

Changes

:bug: The "copy" operation of JSON Patch (RFC 6902) requests that it is an error if the target path points into a non-existing array or object (see #894 for a detailed description). This release fixes the implementation to detect such invalid target paths and throw an exception.

:bug: An array index in a JSON Pointer (RFC 6901) must be an integer. This release fixes the implementation to throw an exception in case invalid array indices such as 10e2 are used.

:white_check_mark: Added the JSON Patch tests from Byron Ruth and Mike McCabe.

:memo: Fixed the documentation of the at(ptr) function with JSON Pointers to list all possible exceptions (see #888).

:memo: Updated the container overview documentation (see #883).

:wrench: The CMake files now respect the BUILD_TESTING option (see #846, #885)

:rotating_light: Fixed some compiler warnings (see #858, #882).

Deprecated functions

:fire: To unify the interfaces and to improve similarity with the STL, the following functions are deprecated since version 3.0.0 and will be removed in the next major version (i.e., 4.0.0):

friend std::istream& operator<<(basic_json&, std::istream&)

friend std::ostream& operator>>(const basic_json&, std::ostream&)

Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.
Source code(tar.gz)
Source code(zip)
json.hpp(501.92 KB)
json.hpp.asc(833 bytes)
v3.0.0(Dec 17, 2017)
Release date: 2017-12-17 SHA-256: 076d4a0cb890a3c3d389c68421a11c3d77c64bd788e85d50f1b77ed252f2a462

Summary

After almost a year, here is finally a new release of JSON for Modern C++, and it is a major one! As we adhere to semantic versioning, this means the release includes some breaking changes, so please read the next section carefully before you update. But don't worry, we also added a few new features and put a lot of effort into fixing a lot of bugs and straighten out a few inconsistencies.

:boom: Breaking changes

This section describes changes that change the public API of the library and may require changes in code using a previous version of the library. In section "Moving from 2.x.x to 3.0.0" at the end of the release notes, we describe in detail how existing code needs to be changed.

The library now uses user-defined exceptions instead of re-using those defined in <stdexcept> (#244). This not only allows to add more information to the exceptions (every exception now has an identifier, and parse errors contain the position of the error), but also to easily catch all library exceptions with a single catch(json::exception).

When strings with a different encoding as UTF-8 were stored in JSON values, their serialization could not be parsed by the library itself, as only UTF-8 is supported. To enforce this library limitation and improve consistency, non-UTF-8 encoded strings now yield a json::type_error exception during serialization (#838). The check for valid UTF-8 is realized with code from Björn Hoehrmann.

NaN and infinity values can now be stored inside the JSON value without throwing an exception. They are, however, still serialized as null (#388).

The library's iterator tag was changed from RandomAccessIterator to BidirectionalIterator (#593). Supporting RandomAccessIterator was incorrect as it assumed an ordering of values in a JSON objects which are unordered by definition.

The library does not include the standard headers <iostream>, <ctype>, and <stdexcept> any more. You may need to add these headers to code relying on them.

Removed constructor explicit basic_json(std::istream& i, const parser_callback_t cb = nullptr) which was deprecated in version 2.0.0 (#480).

:fire: Deprecated functions

To unify the interfaces and to improve similarity with the STL, the following functions are now deprecated and will be removed in the next major version (i.e., 4.0.0):

friend std::istream& operator<<(basic_json&, std::istream&)

friend std::ostream& operator>>(const basic_json&, std::ostream&)

Please use friend std::istream& operator>>(std::istream&, basic_json&) and friend operator<<(std::ostream&, const basic_json&) instead.

:sparkles: New features

With all this breaking and deprecation out of the way, let's talk about features!

We improved the diagnostic information for syntax errors (#301). Now, an exception json::parse_error is thrown which contains a detailed message on the error, but also a member byte to indicate the byte offset in the input where the error occurred.

We added a non-throwing syntax check (#458): The new accept function returns a Boolean indicating whether the input is proper JSON. We also added a Boolean parameter allow_exceptions to the existing parse functions to return a discarded value in case a syntax error occurs instead of throwing an exception.

An update function was added to merge two JSON objects (#428). In case you are wondering: the name was inspired by Python.

The insert function now also supports an iterator range to add elements to an object.

The binary exchange formats CBOR and MessagePack can now be parsed from input streams and written to output streams (#477).

Input streams are now only read until the end of a JSON value instead of the end of the input (#367).

The serialization function dump now has two optional parameters ensure_ascii to escape all non-ASCII characters with \uxxxx and an indent_char parameter to choose whether to indent with spaces or tabs (#654).

Added built-in type support for C arrays (#502), std::pair and std::tuple (#563, #614), enum and enum class (#545), std::vector<bool> (#494). Fixed support for std::valarray (#702), std::array (#553), and std::map<std::string, std::string> (#600, #607).

:hammer: Further changes

Furthermore, there have been a lot of changes under the hood:

Replaced the re2c generated scanner by a self-coded version which allows for a better modularization of the parser and better diagnostics. To test the new scanner, we added millions (8,860,608 to be exact) of unit tests to check all valid and invalid byte sequences of the Unicode standard.

Google's OSS-Fuzz is still constantly fuzz-testing the library and found several issues that were fixed in this release (#497, #504, #514, #516, #518, #519, #575).

We now also ignore UTF-8 byte order marks when parsing from an iterator range (#602).

Values can be now moved from initializer lists (#663).

Updated to Catch 1.9.7. Unfortunately, Catch2 currently has some performance issues.

The non-exceptional paths of the library are now annotated with __builtin_expect to optimize branch prediction as long as no error occurs.

MSVC now produces a stack trace in MSVC if a from_json or to_json function was not found for a user-defined type. We also added a debug visualizer nlohmann_json.natvis for better debugging in MSVC (#844).

Overworked the documentation and added even more examples.

The build workflow now relies on CMake and CTest. Special flags can be chosen with CMake, including coverage (JSON_Coverage), compilation without exceptions (JSON_NoExceptions), LLVM sanitizers (JSON_Sanitizer), or execution with Valgrind (JSON_Valgrind).

Added support for package managers Meson (#576), Conan (#566), Hunter (#671, #829), and vcpkg (#753).

Added CI builders: Xcode 8.3, 9.0, 9.1, and 9.2; GCC 7.2; Clang 3.8, 3.9, 4.0, and 5.0; Visual Studio 2017. The library is further built with C++17 settings on the latest Clang, GCC, and MSVC version to quickly detect new issues.

Moving from 2.x.x to 3.0.0

User-defined Exceptions

There are five different exceptions inheriting from json::exception:

json::parse_error for syntax errors (including the binary formats),

json::invalid_iterator for errors related to iterators,

json::type_error for errors where functions were called with the wrong JSON type,

json::out_of_range for range errors, and

json::other_error for miscellaneous errors.

To support these exception, the try/catch blocks of your code need to be adjusted:

| new exception | previous exception | |:--|:--| | parse_error.101 | invalid_argument | | parse_error.102 | invalid_argument | | parse_error.103 | invalid_argument | | parse_error.104 | invalid_argument | | parse_error.105 | invalid_argument | | parse_error.106 | domain_error | | parse_error.107 | domain_error | | parse_error.108 | domain_error | | parse_error.109 | invalid_argument | | parse_error.110 | out_of_range | | parse_error.111 | invalid_argument | | parse_error.112 | invalid_argument | | invalid_iterator.201 | domain_error | | invalid_iterator.202 | domain_error | | invalid_iterator.203 | domain_error | | invalid_iterator.204 | out_of_range | | invalid_iterator.205 | out_of_range | | invalid_iterator.206 | domain_error | | invalid_iterator.207 | domain_error | | invalid_iterator.208 | domain_error | | invalid_iterator.209 | domain_error | | invalid_iterator.210 | domain_error | | invalid_iterator.211 | domain_error | | invalid_iterator.212 | domain_error | | invalid_iterator.213 | domain_error | | invalid_iterator.214 | out_of_range | | type_error.301 | domain_error | | type_error.302 | domain_error | | type_error.303 | domain_error | | type_error.304 | domain_error | | type_error.305 | domain_error | | type_error.306 | domain_error | | type_error.307 | domain_error | | type_error.308 | domain_error | | type_error.309 | domain_error | | type_error.310 | domain_error | | type_error.311 | domain_error | | type_error.313 | domain_error | | type_error.314 | domain_error | | type_error.315 | domain_error | | out_of_range.401 | out_of_range | | out_of_range.402 | out_of_range | | out_of_range.403 | out_of_range | | out_of_range.404 | out_of_range | | out_of_range.405 | domain_error | | other_error.501 | domain_error |

Handling of NaN and INF

If an overflow occurs during parsing a number from a JSON text, an exception json::out_of_range is thrown so that the overflow is detected early and roundtripping is guaranteed.

NaN and INF floating-point values can be stored in a JSON value and are not replaced by null. That is, the basic_json class behaves like double in this regard (no exception occurs). However, NaN and INF are serialized to null.

Removal of deprecated functions

Function explicit basic_json(std::istream& i, const parser_callback_t cb = nullptr) should be replaced by the parse function: Let ss be a stream and cb be a parse callback function.

Old code:

json j(ss, cb);

New code:

json j = json::parse(ss, cb);

If no callback function is used, also the following code works:

json j; j << ss;

or

json j; ss >> j;
Source code(tar.gz)
Source code(zip)
json.hpp(500.87 KB)
json.hpp.asc(833 bytes)
v2.1.1(Feb 25, 2017)
Release date: 2017-02-25 SHA-256: faa2321beb1aa7416d035e7417fcfa59692ac3d8c202728f9bcc302e2d558f57

Summary

This release fixes a locale-related bug in the parser. To do so, the whole number handling (lexer, parser, and also the serialization) have been overworked. Furthermore, a lot of small changes added up that were added to this release. All changes are backward-compatible.

Changes

:bug: Locales that have a different character than . as decimal separator (e.g., the Norwegian locale nb_NO.UTF-8) led to truncated number parsing or parse errors. The library now has been fixed to work with any locale. Note that . is still the only valid decimal separator for JSON input.

:bug: Numbers like 1.0 were correctly parsed as floating-point number, but serialized as integer (1). Now, floating-point numbers correctly round trip.

:bug: Parsing incorrect JSON numbers with leading 0 (0123) could yield a buffer overflow. This is fixed now by detecting such errors directly by the lexer.

:bug: Constructing a JSON value from a pointer was incorrectly interpreted as a Boolean; such code will now yield a compiler error.

:bug: Comparing a JSON number with 0 led to a comparison with null. This is fixed now.

:bug: All throw calls are now wrapped in macros.

:lock: Starting during the preparation of this release (since 8 February 2017), commits and released files are cryptographically signed with this GPG key. Previous releases have also been signed.

:sparkles: The parser for MessagePack and CBOR now supports an optional start index parameter to define a byte offset for the parser.

:rotating_light: Some more warnings have been fixed. With Clang, the code compiles without warnings with -Weverything (well, it needs -Wno-documentation-unknown-command and -Wno-deprecated-declarations, but you get the point).

:hammer: The code can be compiled easier with many Android NDKs by avoiding macros like UINT8_MAX which previously required defining a preprocessor macro for compilation.

:zap: The unit tests now compile two times faster.

:heavy_plus_sign: Cotire is used to speed up the build.

:pencil2: Fixed a lot of typos in the documentation.

:memo: Added a section to the README file that lists all used third-party code/tools.

:memo: Added a note on constructing a string value vs. parsing.

:white_check_mark: The test suite now contains 11202597 unit tests.

:memo: Improved the Doxygen documentation by shortening the template parameters of class basic_json.

:construction_worker: Removed Doozer.

:construction_worker: Added Codacity.

:arrow_up: Upgraded Catch to version 1.7.2.

Source code(tar.gz)
Source code(zip)
json.hpp(437.42 KB)
json.hpp.asc(801 bytes)
v2.1.0(Jan 28, 2017)
Release date: 2017-01-28

SHA-256: a571dee92515b685784fd527e38405cf3f5e13e96edbfe3f03d6df2e363a767b

Summary

This release introduces a means to convert from/to user-defined types. The release is backwards compatible.

Changes

:sparkles: The library now offers an elegant way to convert from and to arbitrary value types. All you need to do is to implement two functions: to_json and from_json. Then, a conversion is as simple as putting a = between variables. See the README for more information and examples.

:sparkles: Exceptions can now be switched off. This can be done by defining the preprocessor symbol JSON_NOEXCEPTION or by passing -fno-exceptions to your compiler. In case the code would usually thrown an exception, abort() is now called.

:sparkles: Information on the library can be queried with the new (static) function meta() which returns a JSON object with information on the version, compiler, and platform. See the documentation for an example.

:bug: A bug in the CBOR parser was fixed which led to a buffer overflow.

:sparkles: The function type_name() is now public. It allows to query the type of a JSON value as string.

:white_check_mark: Added the Big List of Naughty Strings as test case.

:arrow_up: Updated to Catch v1.6.0.

:memo: Some typos in the documentation have been fixed.

Source code(tar.gz)
Source code(zip)
json.hpp(425.83 KB)
json.hpp.asc(801 bytes)
v2.0.10(Jan 2, 2017)
Release date: 2017-01-02

SHA-256: ec27d4e74e9ce0f78066389a70724afd07f10761009322dc020656704ad5296d

Summary

This release fixes several security-relevant bugs in the MessagePack and CBOR parsers. The fixes are backwards compatible.

Changes

:bug: Fixed a lot of bugs in the CBOR and MesssagePack parsers. These bugs occurred if invalid input was parsed and then could lead in buffer overflows. These bugs were found with Google's OSS-Fuzz, see #405, #407, #408, #409, #411, and #412 for more information.

:construction_worker: We now also use the Doozer continuous integration platform.

:construction_worker: The complete test suite is now also run with Clang's address sanitizer and undefined-behavior sanitizer.

:white_check_mark: Overworked fuzz testing; CBOR and MessagePack implementations are now fuzz-tested. Furthermore, all fuzz tests now include a round trip which ensures created output can again be properly parsed and yields the same JSON value.

:memo: Clarified documentation of find() function to always return end() when called on non-object value types.

:hammer: Moved thirdparty test code to test/thirdparty directory.

Source code(tar.gz)
Source code(zip)
json.hpp(408.60 KB)
json.hpp.asc(801 bytes)

JSON for Modern C++

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