What is the size of an enum in C?


Answers

Taken from the current C Standard (C99): http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf

6.7.2.2 Enumeration specifiers
[...]
Constraints
The expression that defines the value of an enumeration constant shall be an integer constant expression that has a value representable as an int.
[...]
Each enumerated type shall be compatible with char, a signed integer type, or an unsigned integer type. The choice of type is implementation-defined, but shall be capable of representing the values of all the members of the enumeration.

Not that compilers are any good at following the standard, but essentially: If your enum holds anything else than an int, you're in deep "unsupported behavior that may come back biting you in a year or two" territory.

Question

I'm creating a set of enum values, but I need each enum value to be 64 bits wide. If I recall correctly, an enum is generally the same size as an int; but I thought I read somewhere that (at least in GCC) the compiler can make the enum any width they need to be to hold their values. So, is it possible to have an enum that is 64 bits wide?




We have no control over the size of an enum variable. It totally depends on the implementation, and the compiler gives the option to store a name for an integer using enum, so enum is following the size of an integer.




The storage size is not influenced by the amount of the values in enumeration. The storage size is implementation defined, but mostly it is the sizeof(int).




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