operator int()

[diptijain]

what does operator int () in c++ class signifies. I came across a class shown below:

class Foo
  {
    public:
      Foo (int);
      operator int ();
      operator double ();
    private:
      int member_;
  };

  Foo::Foo (int member)
    : member_ (member)
  {
    ;
  }

  Foo::operator int()
  {
    return member_;
  }

  Foo::operator double()
  {
    return 1.0 * member_;
  }

whats the purpose of defining operator int and operator float. As far as i remember C++ prohibits overloading c++ keywords. then how does the above program c\ompiles and works?

[Frost Drake]

Operators are different from keywords, those are conversion operators used to return an equivalent object of one type from another. Kind of like typecasting.

I guess aside from typecasting, all other keywords cannot be overloaded. Since int or double are types, they can be used in conversion operators. Like new and delete for memory.

[grumpy]

An Foo:perator X() (where X is a type) is a conversion operator from Foo to X. There is no constraint that the type be a basic type (int, float, etc). It is also possible to provide conversions to class types by the same means.

So;

//   declaration of Foo from above

int main()
{
      Foo x(42);

      int y = x;    // will invoke  Foo::operator int(), so y will get a value of 42

      float z = x;   // will invoke Foo::operator float() so y will get a single-precision value of 42.0

     y = (int)x;    // explicitly invokes Foo::operator int()
     
}