I can’t find any documentation for functions referenced in SDL_stdinc.h, such as SDL_atoi. Are they supposed to be used?
As I understand it, most of the functions in SDL_stdinc.h is just wrapper functions which, behind the scenes, are executing standard library functions, like atoi for example. Therefore, if you want to find out how a function in SDL_stdinc.h works, you can google for a specific function (for example atoi) and you’ll find out that it’s a c++ function that is used to convert a string to an integer.
atoi documentation: http://www.cplusplus.com/reference/cstdlib/atoi/