I'm a beginner-level C++ programmer, but I understand the concepts of the language fairly well. When I began to learn external C++ libraries, like SDL, OpenGL (maybe something else too), to my great surprise I found out that they don't use C++ concepts at all.
For example, neither SDL, nor OpenGL use classes or exceptions, preferring functions and error codes. In OpenGL I've seen functions like glVertex2f, which takes 2 float variables as an input and probably would be better as a template. Moreover, these libraries sometimes use marcos, while it seems to be a common agreement that using macroses is bad.
All in all, they seem to be written more in C style, than in C++ style. But they are completely different incompaitable languages, aren't they?
The question is: why modern libraries do not use the advantages of the language they are written in?
Best Answer
Both OpenGL and SDL are C libraries and expose a C interface to the rest of the world (as pretty much every language out there can interface with C but not necessarily with C++). Thus, they're restricted to the procedural interface that C gives you and the C way of declaring and using data structures.
Over and above the "interfacing with other languages" aspect that a C interface offers you, C in general tends to be a bit more portable than C++, which in turn makes it easier to get the non-platform dependent part of the code of libraries like these working on another OS or hardware architecture. Pretty much every platform out there has a decent C compiler, but there are still some that have restricted C++ compilers or ones that are just not very good.
While C and C++ are very different languages, they are not "incompatible", in fact, to a large extent C++ is a superset of C. There are some incompatibilities but not many, so using a C interface from C++ is a very easy thing to do.