C++: Iterate through an enum

Question

I just noticed that you can not use standard math operators on an enum such as ++ or +=

So what is the best way to iterate through all of the values in a C++ enum?

Answer 1

You can't with an enum. Maybe an enum isn't the best fit for your situation.

A common convention is to name the last enum value something like MAX and use that to control a loop using an int.

Answer 2

The typical way is as follows:

enum Foo {
  One,
  Two,
  Three,
  Last
};

for ( int foo = One; foo != Last; ++foo )
{
   // ...
}

Of course, this breaks down if the enum values are specified:

enum Foo {
  One = 1,
  Two = 9,
  Three = 4,
  Last
};

This illustrates that an enum is not really meant to iterate through. The typical way to deal with an enum is to use it in a switch statement.

switch ( foo )
{
    case One:
        // ..
        break;
    case Two:  // intentional fall-through
    case Three:
        // ..
        break;
    case Four:
        // ..
        break;
     default:
        assert( ! "Invalid Foo enum value" );
        break;
}

If you really want to enumerate, stuff the enum values in a vector and iterate over that. This will properly deal with the specified enum values as well.

Answer 3

C++ doesn't have introspection, so you can't determine this kind of thing at run-time.

Answer 4

If your enum starts with 0 and the increment is always 1.

enum enumType 
{ 
    A = 0,
    B,
    C,
    enumTypeEnd
};

for(int i=0; i<enumTypeEnd; i++)
{
   enumType eCurrent = (enumType) i;            
}

If not I guess the only why is to create something like a

vector<enumType> vEnums;

add the items, and use normal iterators....

Answer 5

One of many approaches: When enum Just Isn't Enough: Enumeration Classes for C++.

And, if you want something more encapsulated, try this approach from James Kanze.

Answer 6

You can also overload the increment/decrement operators for your enumerated type.