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

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

• GCC
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• MSVC

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).

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).

With clang you can use this:

enum Tristate : char { Yes, No, Maybe };

If you want to typedef, ensure you include the size specifier for both, the enum and the typedef definition:

enum Tristate : char { Yes, No, Maybe };
typedef enum Tristate : char Tristate;

Otherwise you will get a compiler warning.

Or you define an anonymous enum and typedef directly:

typdef enum : char { Yes, No, Maybe } Tristate;