STB libraries are C not C++. Sean Barrett prefers C, basically.

The header-only approach from Sean Barrett is quite a bit different than the header-only approach from C++:

In C++ it means you will be pulling all the code all the time when importing a header.

In C you will get the prototypes for the library. And in only one of the file you will #define STB_<...>_IMPL

Anyhow STB libraries are a joy to work with, I urge anyone to try them