for loop with enum in C++

Question

I have problem trying to make for each loop in C++. I'm not certain is this is possible in C++ if it is I still dont know to make it.

I have one simple problem written in pascal that does finding of the day in year when it is a friday 13 or saturday 25 no metter which day.

In pascal I have code like this:

{First I declare types}
type
    months = (January, February, March, April, May, June, July, August, September, October, November, December);
...
{Then I declare variable for months}
var
    m: mesec;
...
{Then I can declare for loop that will loop over months}
for m:= januar to december do
...

The similar way of doing a for each loop over enumerations is possible in python too. My question is:

Is there any way of doing for or even while loop over enumerations in C++?

I know this may seem as a beginers question but I tried on few different ways to do it doesnt work. Doesnt compile.

http://stackoverflow.com/questions/261963/c-iterate-through-an-enum — Hugo Corrá, Oct 31 '12 at 09:56
http://stackoverflow.com/questions/2479746/loop-on-enumeration-values — Jason, Oct 31 '12 at 09:56

Andriy · Answer 1 · 2012-10-31T10:08:14.677

6

You could do following in c++ provided the enum values are consecutive

enum Months
  {
  January,
  February,
  // etc...
  December,
  Last
  };

for (int month = January; month != Last; ++month)
  {
  // do stuff
  }

edited Oct 31 '12 at 10:08

answered Oct 31 '12 at 09:56

Andriy

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2

But only if enums have consecutive values. – Tio Pepe Oct 31 '12 at 09:58
This stops right before `December` which is incorrect. Generally another enum value is added last called `NumMonths` and you use that. – Pubby Oct 31 '12 at 10:05
Yes enum values are consecutive – MarkoShiva Oct 31 '12 at 10:06

score 4 · Accepted Answer · edited May 23 '17 at 11:54

No, you can't do this directly in C++. There are a few workarounds, though.

If the values of the enum are increased by 1 (i.e. have consecutive values, as they do by default, in case you don't explicitly set their values), you can use them as normal ints, and increase the cycle variable by 1 each time until it equals the last enum's value. This is described in this SO question.
If the values are not increasing by 1 (e.g. enum E {FIRST = 5, SECOND = 10}, it becomes more tricky. You could make an array holding all possible values and use it (that's a crappy solution, but it works):
```
enum E
{
    FIVE = 5,
    TEN = 10,
    THREE = 3
};
E arr[3] = {FIVE,TEN,THREE};
E iterator;
for( int i = 0; i < 3; i++ )
{
    iterator = arr[i];
    //do something with it
}
```

One benefit of this solution is the conciseness of ranged for: `for( E val : arr )`. Depending on your use case, you might benefit from having multiple subsets/orderings of the enum: `E oddValues[] = { THREE, FIVE }; for( E val : oddValues ) ...` — Jonathan Lidbeck, Aug 22 '18 at 16:52

for loop with enum in C++

2 Answers2