Question

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Detecting 64bit compile in C

I want my program to run on both 32 bit and 64 bit Linux OS. So In my C code, I want the compiler to know when it is compiling for a 32 bit and 64 bit architecture. So, I need something like that

#ifdef X64
...
#else
...
#endif

Is there any such define in gcc?

Answer 1

I know of these:

__i386__    
__x86_64__  

I don’t know how reliable they are.

The best option would be adding -DMY_32BIT to the Makefile’s compile line when compiling for 32 bits and checking for MY_32BIT on your code. That way you can be sure.