Detecting 64bit compile in C

Asked 2011-03-11T12:22:35.760

is there a C macro or some kind of way that i can check if my c program was compiled as 64bit or 32bit at compile time in C?

Compiler: GCC Operating systems that i need to do the checks on: Unix/Linux

Also how could i check when running my program if the OS is capable of 64bit?

c linux unix gcc

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2 Answers

Here is the correct and portable test which does not assume x86 or anything else:

#include <stdint.h>
#if UINTPTR_MAX == 0xffffffff
/* 32-bit */
#elif UINTPTR_MAX == 0xffffffffffffffff
/* 64-bit */
#else
/* wtf */
#endif

answered 2011-03-11T13:17:11.310

An easy one that will make language lawyer squeem.

if(sizeof (void *) * CHARBIT == 64) {
...
}
else {
...
}

As it is a constant expression an optimizing compiler will drop the test and only put the right code in the executable.

answered 2011-06-04T16:52:33.707