64 bit enum in C++?

Question

Is there a way to have a 64 bit enum in C++? Whilst refactoring some code I came across bunch of #defines which would be better as an enum, but being greater than 32 bit ca

Answer 1

An enum in C++ can be any integral type. You can, for example, have an enum of chars. IE:

enum MY_ENUM
{
   CHAR_VALUE = 'c',
};

I would assume this includes __int64. Try just

enum MY_ENUM
{
   LARGE_VALUE = 0x1000000000000000,
};

According to my commenter, sixlettervariables, in C the base type will be an int always, while in C++ the base type is whatever is large enough to fit the largest included value. So both enums above should work.

Answer 2

If the compiler doesn't support 64 bit enums by compilation flags or any other means I think there is no solution to this one.

You could create something like in your sample something like:

namespace MyNamespace {
const uint64 LARGE_VALUE = 0x1000000000000000;
};

and using it just like an enum using

MyNamespace::LARGE_VALUE 

or

using MyNamespace;
....
val = LARGE_VALUE;

Answer 3

Enum type is normally determined by the data type of the first enum initializer. If the value should exceed the range for that integral datatype then c++ compiler will make sure it fits in by using a larger integral data type.If compiler finds that it does not belong to any of the integral data type then compiler will throw error. Ref: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1905.pdf
Edit: However this is purely depended on machine architecture

Answer 4

The answers refering to __int64 miss the problem. The enum is valid in all C++ compilers that have a true 64 bit integral type, i.e. any C++11 compiler, or C++03 compilers with appropriate extensions. Extensions to C++03 like __int64 work differently across compilers, including its suitability as a base type for enums.