Detect Windows or Linux in C, C++ [duplicate]

Answer 1

You should use the same #ifdef instead of if(OS_Windows) logic in your code:

#ifdef __unix__         
...
#elif defined(_WIN32) || defined(WIN32) 

#define OS_Windows

#endif

int main(int argc, char *argv[]) 
{
#ifdef OS_Windows
 /* Windows code */
#else
 /* GNU/Linux code */
#endif    
}