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cmacrosc-preprocessorconditional-compilationc89

C89 determine size of int at preprocessor time


I want to compile code conditionally depending on the size of an integer, but I didn't quite find a way to determine the size of an integer in the preprocessor stage.

One idea is using the INT_MAX and comparing it to a constant:

#if INT_MAX >= 9223372036854775807UL
    printf("64 bit\n");
#elif INT_MAX >= 2147483647UL
    printf("32 bit\n");
#else
    printf("16 bit\n");
#endif

But I don't think it is guaranteed that a UL literal can be that large. And ULL is not available in C89 as far as I know.

So do you have any suggestions on how to solve this problem. Is there a macro that contains the size of int in some standard header maybe?

Edit:

Not a duplicate of this question because I don't actually need a generic sizeof and I don't want to print it. I only need to distinguish between distinct integer sizes for conditional compilation.


Solution

  • Testing the smaller values first should work, since the preprocessor uses shortcut evaluation on #if statements:

    #if INT_MAX == 32767
        #error 16 bits
    #elif INT_MAX == 2147483647
        #error 32 bits
    #elif INT_MAX == 9223372036854775807
        #error 64 bits
    #else
        #error "What kind of weird system are you on?"
    #endif