cin to an enum

[jarvisw2]

How do I overload the >> operator to cin to a type enum?

[Cubbi]

same as for any other user-defined type, define std::istream& operator>>(std::istream&, Enum&)

[jarvisw2]

What is the implementation of that function?

[Ganado]

What do you want the user to enter? A string or a number? The whole point of enums is that the number they are shouldn't matter.

// Example program
#include <iostream>
#include <string>

enum Animal {
  Cat = 1,
  Dog = 2,
  Pig = 3
};


std::istream& operator>>(std::istream& is, Animal& animal)
{
    int a;
    is >> a;
    animal = static_cast<Animal>(a);

    return is;
}

int main()
{
    Animal animal;
    std::cin >> animal;

    switch (animal)
    {
      case Pig:
          std::cout << "Pigs are the most equal animal." << std::endl;
          break;
      default:
          std::cout << "Only pigs are allowed to be chosen, sorry!" << std::endl;
          break;
    }
}

[helios]

If you have an enum like

enum Sample{
    First,
    Second,
    Third,
};

and you want to read from the input words like "First", you'll have to do the parsing manually. Unfortunately C++ doesn't have reflection.
Otherwise you can go with something simple like

int val;
if (stream >> val)
    dst = (Sample)val;

[Ganado]

If you want the input to be a string, you have to do something like this. As helios said, C++ doesn't have reflection, so you have to manually make the connection between string "Dog" and enum Dog.

// Example program
#include <iostream>
#include <string>

enum Animal {
  Cat,
  Dog,
  Pig
};

std::istream& operator>>(std::istream& is, Animal& animal)
{
    std::string name;
    is >> name;

    if (name == "Cat")
        animal = Cat;
    else if (name == "Dog")
        animal = Dog;
    else if (name == "Pig")
        animal = Pig;

    return is;
}


int main()
{
    Animal animal;
    std::cin >> animal;

    switch (animal)
    {
      case Pig:
          std::cout << "Pigs are the most equal animal." << std::endl;
          break;
      default:
          std::cout << "Only pigs are allowed to be chosen, sorry!" << std::endl;
          break;
    }
}

edit: fixed code

[jarvisw2]

Great thank you all!