Operator Overloading for Enumerated types

[brad_galloway]

Does anyone know how to overload operators for enumerated types? Such as the operator>>?

[Valmont]

Yes, all you need to do is to pass an identifier of the enum type:

#include <iostream>

using namespace std;

enum MyEnum
{
  NIL, ONE, TWO, THREE
};

ostream& operator<<(ostream& os, const MyEnum& me)
{
  if(me == ONE)
  return os<<1;
  //etcetera
}

int main()
{
  MyEnum theEnum;
  cout<<ONE<<endl;

  cin.get();
  return 0;
}

[brad_galloway]

What about overloading operator>>?

My code is this:

#include<iostream>
using namespace std;

enum station {A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P};
istream& operator>>(istream& is, station& letter){
    is >> letter;
    if(letter == "A")
        return A;
    if(letter == "B")
        return B; 
    if(letter == "C")
        return C; 
    if(letter == "D")
        return D; 
    if(letter == "E")
        return E; 
    if(letter == "F")
        return F; 
    if(letter == "G")
        return G;
    if(letter == "H")
        return H; 
    if(letter == "I")
        return I; 
    if(letter == "J")
        return J; 
    if(letter == "K")
        return K; 
    if(letter == "L")
        return L;                   
    if(letter == "M")
        return M;
    if(letter == "N")
        return N; 
    if(letter == "O")
        return O; 
    if(letter == "P")
        return P; 
 }

It returns an error saying 'ISO C++ forbids comparison between pointer and integer'
'could not convert 'A' to 'std::istream&''

[Valmont]

First rule #1:
For operator >> and << always return the stream at the end:

istream& / ostream& operator<</>>(istream/ostream& iostr, T& t)
{
   //code
   return iostr;
}

Now for your extraction operator:
Are you sure what you are doing? What are you trying to achieve? Something is fishy about overloading an extraction operator for the enum type... do you see why?

As for your answer:
What means this:

#include <iostream>
#include <ios>

using namespace std;

enum AnEnum {A, B, C, D};

int main()
{
  AnEnum MyEnum;
  //What???
  cin>>MyEnum;
  
  //Optional. Depends on IDE: prevents "console flashing".
  cin.get();
  return 0;
}

And this?

  //Come again?
  if(MyEnum == "Hi")
  {
      //Whatever.
  }

With tons of fantasy, I maybe could find a use for overloading the extraction operator for enum types. But you may ask yourself how sane that is .
Many employers threaten to fire programmers if they come up with such code. You have been warned.

[brad_galloway]

Why is insane to overload the operator>>?

Is that just for enum types or overloading it for anything?

[Valmont]

I want you to look again at the two code snippets I gave you. Then I ask you once again:
- do you think that is sane code?
If it is, why Brad? May you can teach me for the occasion .
- do you think fellow coders will understand what you're up to?

You're intelligent enough. Tell me what you think Brad.

[brad_galloway]

With all the stupid questions I have asked I don't see how you can say I'm intellegent. But thank you. And thanks for all the help you have provided. You have helped me revamp my entire coding style.

I guess I should have explained why I was trying to do it. The problem was to a subway router problem in which I had 16 stations identified by letters A-P. I was trying to allow the user to input two letters and then getting the program to solve the route and out put the path of stations they need to take. Although I could write a different function to do so. There are other ways than overloading the operator>>.

I'm still in the habit of trying to break out of my text-book way of thinking and becoming a more flexible programmer.

[Valmont]

Well, just think of overloaded operators as conveniance functions. So find an easy (canonical) solution first, then see of operator overloading makes the code neater. Otherwise don't bother.