This is a typical idiom frequently seen in modern C and C++ codes. As https://github.com/krychu/wfc#how-to-use-the-library says, you need to define a macro in a C file in order to "expand" the actual code there.
Having the code in the header gives a bit more flexibility considering the file layout. IMHO this is an awkward consequence of the missing de-facto-standard in C/C++ build systems.
Having the code in the header gives a bit more flexibility considering the file layout. IMHO this is an awkward consequence of the missing de-facto-standard in C/C++ build systems.