Very low footprint JSON parser written in portable ANSI C

Related tags

JSON json-parser

Very low footprint JSON parser written in portable C89 (sometimes referred to as ANSI C).

  • BSD licensed with no dependencies (i.e. just drop the C file into your project)
  • Never recurses or allocates more memory than it needs
  • Very simple API with operator sugar for C++

Build Status

Want to serialize? Check out json-builder!


There is now a makefile which will produce a libjsonparser static and dynamic library. However, this is not required to build json-parser, and the source files (json.c and json.h) should be happy in any build system you already have in place.


json_value * json_parse (const json_char * json,
                         size_t length);

json_value * json_parse_ex (json_settings * settings,
                            const json_char * json,
                            size_t length,
                            char * error);

void json_value_free (json_value *);

The type field of json_value is one of:

  • json_object (see u.object.length, u.object.values[x].name, u.object.values[x].value)
  • json_array (see u.array.length, u.array.values)
  • json_integer (see u.integer)
  • json_double (see u.dbl)
  • json_string (see u.string.ptr, u.string.length)
  • json_boolean (see u.boolean)
  • json_null

Compile-Time Options

Unless otherwise specified, compile definitions must be provided both when compiling json.c and when compiling any of your own source files that include json.h.


Stores the source location (line and column number) inside each json_value.

This is useful for application-level error reporting.


By default, json_int_t is defined as long under C89 and int_fast64_t otherwise. For MSVC it is defined as __int64 regardless of language standard support.

Optionally, you may define json_int_t to be your own preferred type name for integer types parsed from JSON documents. It must be a signed integer type, there is no support for unsigned types. If you specify a raw primitive type without signed or unsigned (and not a typdef), JSON_INT_MAX will be calculated for you. Otherwise, you must provide your own definition of JSON_INT_MAX as the highest positive integer value that can be represented by json_int_t.

Example usage:

  • -Djson_int_t=short
  • "-Djson_int_t=signed char" -DJSON_INT_MAX=127
  • "-Djson_int_t=long long"
  • -Djson_int_t=__int128

Runtime Options

settings |= json_enable_comments;

Enables C-style // line and /* block */ comments.

size_t value_extra

The amount of space (if any) to allocate at the end of each json_value, in order to give the application space to add metadata.

void * (* mem_alloc) (size_t, int zero, void * user_data);
void (* mem_free) (void *, void * user_data);

Custom allocator routines. If NULL, the default malloc and free will be used.

The user_data pointer will be forwarded from json_settings to allow application context to be passed.

Changes in version 1.1.0

  • UTF-8 byte order marks are now skipped if present

  • Allows cross-compilation by honoring --host if given (@wkz)

  • Maximum size for error buffer is now exposed in header (@LB--)

  • GCC warning for static after const fixed (@batrick)

  • Optional support for C-style line and block comments added (@Jin-W-FS)

  • name_length field added to object values

  • It is now possible to retrieve the source line/column number of a parsed json_value when JSON_TRACK_SOURCE is enabled

  • The application may now extend json_value using the value_extra setting

  • Un-ambiguate pow call in the case of C++ overloaded pow (@fcartegnie)

  • Fix null pointer de-reference when a non-existing array is closed and no root value is present

  • json fails on double value

    json fails on double value

    Fails with 1:104: Unexpected . in object

    { "status": "ok", "results": [ { "recordings": [ { "id": "889ec8e0-b8a6-4ff1-a104-5512ea49fe87" } ], "score": 0.879051, "id": "45047cb1-3d3f-477e-a3dc-f14e8254e78d" } ] }

    opened by fcartegnie 9
  • Testing flags may not be correct.

    Testing flags may not be correct.

    VS2013 flagged a couple of possible issues and I'm not sure it it's right or not. Line 411:

    else if (!state.settings.settings & json_relaxed_commas)

    parses as ((!state.settings.settings) & json_relaxed_commas) and I think maybe it should be (!(state.settings.settings & json_relaxed_commas))

    And likewise line 572:

    if (flags & flag_need_comma && (!state.settings.settings & json_relaxed_commas))
    opened by ghost 7
  • Fix strict-aliasing warning

    Fix strict-aliasing warning

    A couple of lines trigger strict-aliasing warnings on gcc (Ubuntu)

    error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]

    Output of gcc --version

    gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

    This PR addresses those two warnings

    Commit d7b67db02aaa17fcc9bfbc8b60f41c3b677bd5a8 also simplifies the pointer notation by removing a reference and a dereference that seem to cancel each other out. Let's say that value->u.object.values is a pointer in memory location A and points to location B. Then | expression | type | pointer location | pointed location | |---|---|---|---| | value->u.object.values | json_object_entry * | A | B | | &value->u.object.values | json_object_entry ** | | A | | (char **) &value->u.object.values | char ** | | A | | *(char **) &value->u.object.values | char * | | B |

    The last expression can be simplified in (char *) value->u.object.values

    opened by ChromaticIsobar 5
  • Improve calculation of JSON_INT_MAX

    Improve calculation of JSON_INT_MAX

    From That value can be calculated mathematically using 2**((n * 8) - 1) - 1. Which can also be done using the following bit shift:

    static const json_int_t JSON_INT_MAX = (1L << ((8 * sizeof(json_int_t) - 1))) - 1
    opened by trevnorris 5
  • Parse error when arrays are empty

    Parse error when arrays are empty


    The parser fails when the following JSON is provided: {"myArray": [] }

    In code: static char str[] = "{ "myArray": [] }"; json_value * root = json_parse(str, strlen(str));

    This is because malloc is called with a size of 0, due to the empty array. However some implementations of malloc will return NULL when asked to allocate 0 bytes and in this case the parser stops. I think this is wrong. In my opinion the parser should not try to allocate 0 bytes. A simple check in the newValue method for the json_array case can prevent this:

    In code: if (value->u.array.length == 0) { break; }

    With these three lines of code the parser can also handle the above input.

    Regards, Matthijs

    opened by mboelstra 5
  • Portability issue: cast from pointer to unsigned long

    Portability issue: cast from pointer to unsigned long

    The compiler on my system is 64 bit and sizeof(void *) is 8.

    json-parser\json.c: In function 'new_value':
    json-parser\json.c:135:42: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
                       (state, values_size + ((unsigned long) value->u.object.values), 0)) )
 In context, I'm not sure what this is supposed to be doing, so I don't have a proposed solution.

    opened by LB-- 5
  • Compile error using clang

    Compile error using clang

    [100%] Building C object AudioAgent/external/CMakeFiles/JsonParser.dir/json-parser/json.c.o cc: warning: argument unused during compilation: '-no-cpp-precomp' /Users/johank/safe/audio/trunk/AudioAgent/external/json-parser/json.c:42:51: error: missing field 'type' initializer [-Werror,-Wmissing-field-initializers] const struct _json_value json_value_none = { 0 }; ^ I would suggest changing to

    const struct _json_value json_value_none;

    since static variables should anyway be zero initialized by default.

    opened by jkotlinski 5
  • Raisonance RC51 error

    Raisonance RC51 error


    I just tried compiling this with Raisonance's RC51 compiler, and it threw this error:

    *** ERROR C203 IN LINE 638 OF json.c : '(XDATA  CODE)': pointer: different mspace

    on the first lines of e_failed.

    With those lines commented out it worked fine.

    opened by fbstj 5
  • Use size_t for memory size

    Use size_t for memory size

    The C standard library consistently uses size_t for variables related to memory size. See for example malloc(), memset(), sizeof().

    The maximum value of an object of size_t type is:

    Note that we cannot change unsigned longto size_t everywhere without modifying the API, so we will probably have to live with this exception:

    typedef struct
       unsigned long max_memory;
    } json_settings;
    opened by DimitriPapadopoulos 4
  • Copyright dates and web site updates

    Copyright dates and web site updates

    Perhaps it's time we change:

     * Copyright (C) 2012, 2013, 2014, 2016, 2018, 2019, 2021 James McLaughlin et al.  All rights reserved.


     * Copyright (C) 2012-2021 James McLaughlin et al.  All rights reserved.
    opened by DimitriPapadopoulos 4
  • Fix header files

    Fix header files

    json.h: <inttypes.h><stdint.h> int64_t is defined in <stdint.h>, no need for the full <inttypes.h>

    json.h: <stdlib.h><stddef.h> <stddef.h> is enough to define size_t

    json.c: <stdlib.h> Now that <stdlib.h> has been removed from json.h, add it to json.c for malloc()/calloc() and free()

    opened by DimitriPapadopoulos 4
  • Add ASan and UBSan to CI

    Add ASan and UBSan to CI

    When built with UndefinedBehaviorSanitizer and AddressSanitizer the tests throw this UndefinedBehaviorSanitizer error

     json.c:437:34: runtime error: applying non-zero offset 8 to null pointer
        #0 0x4caab2 in json_parse_ex /home/runner/work/json-parser/json-parser/json.c:437:34
        #1 0x4daf8c in json_test /home/runner/work/json-parser/json-parser/tests/test.c:79:18
        #2 0x4da892 in json_verify /home/runner/work/json-parser/json-parser/tests/test.c:153:14
        #3 0x4d9fe2 in main /home/runner/work/json-parser/json-parser/tests/test.c:229:12
        #4 0x7f148b3dc0b2 in __libc_start_main (/lib/x86_64-linux-gnu/
        #5 0x41c2fd in _start (/home/runner/work/json-parser/json-parser/json-test+0x41c2fd)

    Should be fixed first then this CI could help making sure it wont happen again :slightly_smiling_face:

    opened by ChillerDragon 0
  • `json_char` and `strcmp()`

    `json_char` and `strcmp()`

    In this piece of code, name is of type json_char * but strcmp() operates on char *:

    Could this be an issue? What are the expected / valid definitions of json_char?

    opened by DimitriPapadopoulos 1 is the official code repository for json-c. See the wiki for release tarballs for download. API docs at

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