enums and bit fields

[Randy Budd]

can I use enums for a bit field (as opposed to an int)?

is it valid at all?

is it undefined across platforms? (i.e. not very portable)

is it ok as long as the enums don't overrun the bitfield?

is an enum signed or unsigned?

EX

typedef enum {
TYPE_A, TYPE_B, TYPE_C,
} Type;

typedef struct {
unsigned int aType:5;
Type bType:5; /* is this O.K. ? */
unsigned int aFlag:1;
} Struct;

main()
{
Struct a;

a.aType = TYPE_B;
a.bType = TYPE_C;

....

}

 

[Keith Thompson]

can I use enums for a bit field (as opposed to an int)?

Not portably. C99 6.7.2.1p4:

A bit-field shall have a type that is a qualified or unqualified
version of _Bool, signed int, unsigned int, or some other
implementation-defined type.

is it valid at all?

is it undefined across platforms? (i.e. not very portable)

is it ok as long as the enums don't overrun the bitfield?

is an enum signed or unsigned?

These are all implementation-defined.

[...]

main()

Make this "int main(void)".

[...]