GCC/Clang/MSVC extension for specifying C enum size?

Question

Is there any extension feature to specify size of C enum on each compiler?

• GCC
• Clang
• MSVC

Answer 1

With GCC, you cannot specify the exact length, but you can have it take up the shortest length possible with -fshort-enums. Example:

#include <stdio.h>

typedef enum
{
    f1, f2
} foo;

int main()
{
    printf("%i\n", sizeof(foo));
    return 0;
}

Compile:

gcc program.c -fshort-enums

Output:

1

However, if you ever want to link to anything, you have to make sure that whoever looks at your headers also uses -fshort-enums or it will not be ABI compliant (and you will see some really funny errors).

Answer 2

C++11 introduced a standardized way to do this, but since this is C you'll have to settle for a more simple method of making the last enum INT_MAX or a value thats large enough so that only the type you want can hold it (this is what the DirectX SDK does). Unfortunatly there is no way to force a maximum size (at least not without compiler specific extensions).