mongo-c-driver | The Official MongoDB driver for C language

Document size is limited to 16 MB, which fits in a signed 32-bit integer with room to spare.

While document size limits larger than 16 MB were considered, my guess is there was no serious consideration of document sizes exceeding 2 GB, therefore the difference in range afforded by using unsigned 32-bit integers for length wasn't a meaningful benefit.

Thus, there is no reason to use an unsigned type.

Reasons to NOT use an unsigned type:

• Wraparound potential from UINT_MAX to 0.
• -1 could be used as a special designator.

The function you located is indeed used for executing tests (cross-driver ones) which do contain a findOne operation.

Based on this I would say the C driver doesn't provide a findOne operation and you are meant to use something like the find_one function you found to get a single document out of the cursor returned from mongoc_collection_find_with_opts.

From Tutorial for mongocxx:

IMPORTANT: Before making any connections, you need to create one and only one instance of mongocxx::instance. This instance must exist for the entirety of your program.

So, you can add this as a static member of your MongoDB class:

header

The answer seems to be in the installation guide, I missed a step:

For building with Visual Studio 2017 (without a C++17 polyfill), it is necessary to configure with an additional option, /Zc:__cplusplus to opt into the correct definition of __cplusplus (problem described here):

'C:\Program Files (x86)\CMake\bin\cmake.exe' ..
-G "Visual Studio 15 2017 Win64"
-DCMAKE_CXX_STANDARD=17
-DCMAKE_CXX_FLAGS="/Zc:__cplusplus"
-DCMAKE_PREFIX_PATH=C:\mongo-c-driver
-DCMAKE_INSTALL_PREFIX=C:\mongo-cxx-driver \

I added the "/Zc:__cplusplus" flag as required and it compiled fine!

If you check the cmake file generated, you can see this block:

The answer is that the mongodb-cxx driver for MinGW is not supported: https://developer.mongodb.com/community/forums/t/undefined-reference-to-bsoncxx-when-try-to-compile/2896/4?u=alexxanderx

The tutorial for building mongo-c-driver on Windows is missing the step which source should be downloaded (as the paragraphs for other platforms provide). So one might be tempted to download Source code (zip) from the releases page. This will only get you a copy of the repository when the tag was set. But it is essential to use the mongo-c-driver-1.16.2.tar.gz link on the releases page. Then everything should work.