Detecting 64bit compile in C

Question

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 n

Answer 1

A compiler and platform neutral solution would be this:

// C
#include <stdint.h>

// C++
#include <cstdint>

#if INTPTR_MAX == INT64_MAX
// 64-bit
#elif INTPTR_MAX == INT32_MAX
// 32-bit
#else
#error Unknown pointer size or missing size macros!
#endif

Avoid macros that start with one or more underscores. They are not standard and might be missing on your compiler/platform.

Answer 2

Since you tagged this "gcc", try

#if __x86_64__
/* 64-bit */
#endif

Answer 3

Use this UINTPTR_MAX value to check build type.

#include <stdio.h>
#include <limits.h>

#if UINTPTR_MAX == 0xffffffffffffffffULL               
# define BUILD_64   1
#endif

int main(void) {

    #ifdef BUILD_64
    printf("Your Build is 64-bit\n");

    #else
    printf("Your Build is 32-bit\n");

    #endif
    return 0;
}