operator overloading for enum type

Question

Consider the following code:

#include<iostream>


enum week
{
    sun=1,
    mon,
    tue,
    wed,
    thr,
    fri,
    sat
};


week &operator++(week& day,int)
{
    if(day==sat)
        day=sun;
    else
        day++; // This expression
   return day;
}


int main()
{
    week day=sun;
    for(int i=0;i<=10;i++,day++)
    {
        std::cout<<day;
    }
}

In the expression day++ it goes into infinite recursion.

If I cast it like ((int)day)++ the compiler gives the following error:

      error: lvalue required as increment operand

If I change the line to day=week(((int)day)+1) it works. But how to fix the above code so it works with the ++ operator?

Why do you insist on ++ operator. What's wrong with day=week(((int)day)+1);? You can also write simply return day = week(((int)day%7)+1);. — Daniel Langr
– Daniel Langr, Commented Dec 16, 2019 at 14:28
I would ask for is there any option available for using ++ operator. — srilakshmikanthanp
– srilakshmikanthanp, Commented Dec 16, 2019 at 14:30
Unscoped enumerations are basically glorified symbolic integer constants. You might have better luck with stronger typed scoped enumerations. — Some programmer dude
– Some programmer dude, Commented Dec 16, 2019 at 14:32
I suggest not relying on self-modifying ++ as much. week next(week day) { if (day==sat) return sun; return week(((int)day)+1); and in the for loop, use day = next(day). — Eljay
– Eljay, Commented Dec 16, 2019 at 15:10
In addition to what everyone else said, your POST-increment operator is returning the wrong value anyway. POST-increment (day++) is supposed to return a copy of the previous value prior to incrementing. Your code is more suited for a PRE-increment (++day) operator instead, which returns a reference to the modified value. See Increment/decrement operators for more details — Remy Lebeau
– Remy Lebeau, Commented Dec 16, 2019 at 16:56

L. Scott Johnson · Accepted Answer · 2019-12-16 14:27:32Z

5

The default increment operator doesn't work well with enums. You'll have to overload the increment operator (with your week(((int)day)+1) logic) and handle the wrap-around in that overload function instead.

answered Dec 16, 2019 at 14:27

L. Scott Johnson

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Bathsheba · Accepted Answer · 2019-12-16 14:30:45Z

4

One way round the compiler error is to cast to a reference instead

((int&)day)++;

but you should take care that the backing type of the enum is an int:

enum week : int
{
    // and so on

If that's not to your taste and would rather have the compiler decide the backing type for you then use

((std::underlying_type<week>::type&)day)++;

answered Dec 16, 2019 at 14:30

Bathsheba

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Hawky · Accepted Answer · 2019-12-16 14:30:33Z

4

(int)day returns an int, which you try to increment by ++ operator. So basically you do something like ... = 5++ which is not legal.

answered Dec 16, 2019 at 14:30

Hawky

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