detect reliably Mac OS X, iOS, Linux, Windows in C preprocessor

Problem And Question

If here’s some cross-platform C/C++ code should be compiled on Mac OS X, iOS, Linux, Windows, how can I detect them reliably during preprocessor process?

Best Solution And Answer

There are predefined macros that are used by most compilers, you can find the list [here]. GCC compiler predefined macros can be found [here].
Here is an example for gcc:

#ifdef _WIN32
   //define something for Windows (32-bit and 64-bit, this part is common)
   #ifdef _WIN64
      //define something for Windows (64-bit only)
   #endif
#elif __APPLE__
    #include "TargetConditionals.h"
    #if TARGET_IPHONE_SIMULATOR
         // iOS Simulator
    #elif TARGET_OS_IPHONE
        // iOS device
    #elif TARGET_OS_MAC
        // Other kinds of Mac OS
    #else
        // Unsupported platform
    #endif
#elif __linux
    // linux
#elif __unix // all unices not caught above
    // Unix
#elif __posix
    // POSIX
#endif

This defined macroses depends on compiler that you are going to use.

The _WIN64 #ifdef can be nested into the _WIN32 #ifdef because _WIN32 is defined when targeting Windows, not only the x86 version. This prevents code duplication if some includes are common to both.