How to use strongly typed enums

Question

I'm not able to compile the following program:

#include <iostream>

using namespace std;

enum class my_enum
{
    ANT,
    BAT,
    CAT,
    DOG,
    EGG,
    FAN,
    MAX_MEMBERS
};

int main(int argc, char * argv[])
{
    my_enum i = my_enum::ANT;

    for(i = my_enum::ANT; i < my_enum::MAX_MEMBERS; i++)
    {
        cout << "Enum value = " << i << endl;
    }

    return 0;
}

I see the build error as follows:

error: no ‘operator++(int)’ declared for postfix ‘++’ [-fpermissive] for(i = my_enum::ANT; i < my_enum::MAX_MEMBERS; i++)

possible duplicate of [How can I iterate over an enum?](http://stackoverflow.com/questions/261963/how-can-i-iterate-over-an-enum) — mpromonet, Feb 22 '15 at 10:01

score 1 · Accepted Answer · answered Feb 24 '15 at 13:31

Although incrementation operators are not defined for enumerated types by default, you can define your own, for instance:

my_enum& operator++(my_enum& i)
{
    assert(i < my_enum::MAX_MEMBERS);
    i = static_cast<my_enum>(static_cast<int>(i)+1);
    return i;
}

You can then write ++i in your loop and it will compile happily.

KarteekKumarM · Answer 2 · 2015-02-22T10:09:39.517

You are assuming that you can use my_enum as an int, but it now a new type. So the "++" operator and the "<<" operator need to be defined for this type to work.

A simple way to work around this is :

#include <iostream>

using namespace std;

enum class my_enum
{
    ANT,
    BAT,
    CAT,
    DOG,
    EGG,
    FAN,
    MAX_MEMBERS
};

int main( int argc, char * argv[] )
{
    for ( my_enum i = my_enum::ANT; i < my_enum::MAX_MEMBERS;  )
    {
        cout << "Enum value = " << (int)i << endl;
        i = my_enum( (int)i + 1 );
    }

    return 0;
}

However, normally to iterate over an enum, typical code would be :

#include <iostream>

using namespace std;

enum my_enum
{
    ANT,
    BAT,
    CAT,
    DOG,
    EGG,
    FAN,
    MAX_MEMBERS
};

int main( int argc, char * argv[] )
{
    for ( int i = my_enum::ANT; i < my_enum::MAX_MEMBERS; i++ )
    {
        cout << "Enum value = " << i << endl;
    }

    return 0;
}

How to use strongly typed enums

2 Answers2