Hi, I am trying yo use lmdb++ to work with LMDB. I have it working via the example you provided. I have a problem when trying to use cursor_put with MDB_MULTIPLE. I cant seem to get it to work right. Here is the code:

`std::vector rawData(1000000, std::rand()); MDB_val value1, value2, key; value1.mv_size = sizeof(int); value1.mv_data = const_cast<void*> (static_cast<const void*> (&rawData[0]));; value2.mv_size = 1000000; MDB_val mData[2] = { value1, value2 }; int i = 0;

auto env = lmdb::env::create(); env.set_mapsize(1UL * 1024UL * 1024UL * 1024UL); /* 1 GiB */ env.open(path.c_str(), 0, 0664); auto wtxn = lmdb::txn::begin(env); auto dbi = lmdb::dbi::open(wtxn, nullptr, MDB_DUPSORT | MDB_DUPFIXED | MDB_INTEGERDUP | MDB_CREATE); auto cursor = lmdb::cursor::open(wtxn, dbi); key.mv_size = sizeof(i); key.mv_data = &i; cursor_put(cursor, &key, mData, MDB_MULTIPLE);`

I think I am probably misusing the lib or some part of it. So any advice would be good.

I'd like to use lmdb++ but as it stands I cannot because of it's dependency on pthreads... The real problem is that on Windows it looks like the current code requires pthread_t from mingw and I am using Visual Studio on Windows. Since it requires a modern implementation of C++ anyway, might it be possible to use only standard features?

dbi_put return false if it cannot insert a duplicate value because of MDB_NODUPDATA or MDB_NOOVERWRITE, while cursor_put will raise an exception.

This patch modifies cursor_put so it has the same behavior as dbi_put.

In the example code provided in your Readme.MD, the second transaction uses the "dbi" instance that was opened using the first transaction:

auto dbi = lmdb::dbi::open(wtxn, nullptr);
...
auto cursor = lmdb::cursor::open(rtxn, dbi);

Is this recommended? Or should one open a new database for every transaction?

I tried to compile your example.cc using the latest lmdb++.h in /usr/include like so:

g++ example.cc

But I get the followin error:

/tmp/ccUhugbK.o: In function `lmdb::env_create(MDB_env**)':
example.cc:(.text+0x14): undefined reference to `mdb_env_create'
/tmp/ccUhugbK.o: In function `lmdb::env_open(MDB_env*, char const*, unsigned int, unsigned int)':
example.cc:(.text+0x5b): undefined reference to `mdb_env_open'
/tmp/ccUhugbK.o: In function `lmdb::env_close(MDB_env*)':
example.cc:(.text+0x8e): undefined reference to `mdb_env_close'
/tmp/ccUhugbK.o: In function `lmdb::env_set_flags(MDB_env*, unsigned int, bool)':
example.cc:(.text+0xc8): undefined reference to `mdb_env_set_flags'
/tmp/ccUhugbK.o: In function `lmdb::env_set_mapsize(MDB_env*, unsigned long)':
example.cc:(.text+0x106): undefined reference to `mdb_env_set_mapsize'
/tmp/ccUhugbK.o: In function `lmdb::txn_begin(MDB_env*, MDB_txn*, unsigned int, MDB_txn**)':
example.cc:(.text+0x14f): undefined reference to `mdb_txn_begin'
/tmp/ccUhugbK.o: In function `lmdb::txn_commit(MDB_txn*)':
example.cc:(.text+0x182): undefined reference to `mdb_txn_commit'
/tmp/ccUhugbK.o: In function `lmdb::txn_abort(MDB_txn*)':
example.cc:(.text+0x1b5): undefined reference to `mdb_txn_abort'
/tmp/ccUhugbK.o: In function `lmdb::dbi_open(MDB_txn*, char const*, unsigned int, unsigned int*)':
example.cc:(.text+0x1e6): undefined reference to `mdb_dbi_open'
/tmp/ccUhugbK.o: In function `lmdb::dbi_put(MDB_txn*, unsigned int, MDB_val const*, MDB_val*, unsigned int)':
example.cc:(.text+0x239): undefined reference to `mdb_put'
/tmp/ccUhugbK.o: In function `lmdb::cursor_open(MDB_txn*, unsigned int, MDB_cursor**)':
example.cc:(.text+0x28b): undefined reference to `mdb_cursor_open'
/tmp/ccUhugbK.o: In function `lmdb::cursor_close(MDB_cursor*)':
example.cc:(.text+0x2be): undefined reference to `mdb_cursor_close'
/tmp/ccUhugbK.o: In function `lmdb::cursor_get(MDB_cursor*, MDB_val*, MDB_val*, MDB_cursor_op)':
example.cc:(.text+0x2ef): undefined reference to `mdb_cursor_get'
/tmp/ccUhugbK.o: In function `lmdb::error::what() const':
example.cc:(.text._ZNK4lmdb5error4whatEv[_ZNK4lmdb5error4whatEv]+0x1c): undefined reference to `mdb_strerror'
collect2: error: ld returned 1 exit status

Looking inside lmdb++.h it seems that mdb_env_create hasn't been defined anywhere, but it IS referenced.

PS: Thanks for this great library, I hope to make use of it.

Error is "lmdb++.h:97:12: error: thread-local storage is not supported for the current target static thread_local char buffer[1024];"

Apple LLVM version 7.0.2 (clang-700.1.81) Target: x86_64-apple-darwin15.2.0 Thread model: posix

In my case, I'm storing key/value pairs as int/string.

The problem arises when I wan't to check if given pair exists in database. Currently I'm only able to check if given key exists via lmdb::cursor::find. Is it somehow possible to do this for key/value pair?

Hello,

while trying to compile on windows I ran into a few minor issues.

Mainly because Microsoft has not updated __cplusplus for years.

For some odd reason it does not think lmdb::val is a POD. Given the info on PODTypes on CppReference I'd guess it's still doing pre-11 checks or the default-declared dtor confuses him.

My testings were done with VS2015, which afaik is fully compliant with c++11.

in lmdb::dbi_put there is no way to put an element like : int data[10] lmdb::val lmdbData((void*)data, sizeof(int)*10 ); ... dbi.put(wtxn, "data", lmdbData))

Hi Here is my contribution to your code, its working good on powersystems.

Thanks for the code, its working good.

What do these changes do?

Added Architecture "ppc64le"

Are there changes in behavior for the user?

No

@core-process noticed and fixed this issue in our C++17 fork of lmdbxx:

If an exception was throw by txn.commit() (ie MDB_MAP_FULL), and this transaction was later aborted (because it went out of scope while unwinding the stack), then a double-free would occur.

You can use the following test to observe this (address sanitizer should be enabled, as it is by default in our Makefile):

https://github.com/hoytech/lmdbxx/blob/5223582ebf92a9b14608ce6768535aef0c65910f/check.cc#L329

Weird output from cursor get: I would get both key and value inside the key variable, then the value inside the value variable :

#include <cstdio>
#include <cstdlib>
#include <lmdb++.h>
using namespace lmdb;
int getsize(const lmdb::env& e){
    auto t = lmdb::txn::begin(e.handle(), nullptr, MDB_RDONLY);
    auto d = lmdb::dbi::open(t, nullptr);
    int r=d.size(t);
    t.abort();
    return r;
}


int main() {
  auto env = lmdb::env::create();
  env.set_mapsize(1UL * 1024UL * 1024UL * 1024UL); /* 1 GiB */
  env.open("./example.mdb", 0, 0664);
  {
    auto wtxn = lmdb::txn::begin(env);
    auto dbi = lmdb::dbi::open(wtxn, nullptr);
    char a[6] = "hello";
    dbi.put(wtxn, "email", "hello");
    dbi.put(wtxn, "key", "value");
    dbi.put(wtxn, "user", "johndoe");
    wtxn.commit();
  }
  {
      auto rtxn = lmdb::txn::begin(env);
      auto dbi = lmdb::dbi::open(rtxn, nullptr);
      auto cursor = lmdb::cursor::open(rtxn, dbi);
      lmdb::val k, v;
      while(cursor.get(k, v, MDB_NEXT)){
        printf("We got '%s'\nValue '%s'\n", k.data(), v.data());
      }
  }
  {
    std::printf("size is %d\n", getsize(env));
  }
return EXIT_SUCCESS;
}

Expected Output:

We got 'email'
Value 'hello'
We got 'key'
Value 'value'
We got 'user'
Value 'johndoe'
size is 3

Output :

We got 'emailhello'
Value 'hello'
We got 'keyvalue'
Value 'value'
We got 'userjohndoe'
Value 'johndoe'
size is 3

I tried to simply delete an entry, and can't really know if I'm wrong or if this is a bug, the only documentation I could find was the api reference, if anyone has better material I'd be glad to take it.

#include <cstdio>
#include <cstdlib>
#include <lmdb++.h>
using namespace lmdb;
int main() {
  auto env = lmdb::env::create();
  env.set_mapsize(1UL * 1024UL * 1024UL); 
  env.open("./example.mdb", 0, 0664);

  auto wtxn = lmdb::txn::begin(env);
  auto dbi = lmdb::dbi::open(wtxn, nullptr);
  dbi.put(wtxn, "key_entry", "value_entry");
  wtxn.commit();
  dbi.del(wtxn, "key_entry");

  return EXIT_SUCCESS;
}

This yields the following error :

terminate called after throwing an instance of 'lmdb::runtime_error'
  what():  mdb_del: Invalid argument