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?
C Enums – What is the Size of an Enum in C?
c++enums
Related Solutions
If you don't assign your enums you can do somethings like this:
enum MyType {
Type1,
Type2,
Type3,
NumberOfTypes
}
NumberOfTypes will evaluate to 3 which is the number of real types.
This is a C++ interview test question not homework.
Then your interviewer needs to refresh his recollection with how the C++ standard works. And I quote:
For an enumeration whose underlying type is not fixed, the underlying type is an integral type that can represent all the enumerator values defined in the enumeration.
The whole "whose underlying type is not fixed" part is from C++11, but the rest is all standard C++98/03. In short, the sizeof(months_t) is not 4. It is not 2 either. It could be any of those. The standard does not say what size it should be; only that it should be big enough to fit any enumerator.
why the all size is 4 bytes ? not 12 x 4 = 48 bytes ?
Because enums are not variables. The members of an enum are not actual variables; they're just a semi-type-safe form of #define. They're a way of storing a number in a reader-friendly format. The compiler will transform all uses of an enumerator into the actual numerical value.
Enumerators are just another way of talking about a number. january is just shorthand for 0. And how much space does 0 take up? It depends on what you store it in.
Best Answer
Taken from the current C Standard (C99): http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf
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.
Update: The latest publicly available draft of the C Standard (C11): http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1570.pdf contains the same clauses. Hence, this answer still holds for C11.