Compilation fails with unknown type name 'size_t' on Windows

[Isty001]

Here the compilation fails, because size_t is not defined. Probably it worked elsewhere because it was included somewhere previously.

I'm not sure about this though:

#if defined (__unix__) || (defined (__APPLE__) && defined (__MACH__))
#include <unistd.h>
#endif

I think it can be simply replaced by #include <stdlib.h> and will work on every platform.