How can I use cout << myclass

问题:

myclass is a C++ class written by me and when I write:

myclass x;
cout << x;

How do I output 10 or 20.2, like an integer or a float value?

回答1:

Typically by overloading operator<< for your class:

struct myclass { 
    int i;
};

std::ostream &operator<<(std::ostream &os, myclass const &m) { 
    return os << m.i;
}

int main() { 
    myclass x(10);

    std::cout << x;
    return 0;
}

回答2:

You need to overload the << operator,

std::ostream& operator<<(std::ostream& os, const myclass& obj)
{
      os << obj.somevalue;
      return os;
}

Then when you do cout << x (where x is of type myclass in your case), it would output whatever you've told it to in the method. In the case of the example above it would be the x.somevalue member.

If the type of the member can't be added directly to an ostream, then you would need to overload the << operator for that type also, using the same method as above.

回答3:

it's very easy, just implement :

std::ostream & operator<<(std::ostream & os, const myclass & foo)
{
   os << foo.var;
   return os;
}

You need to return a reference to os in order to chain the outpout (cout << foo << 42 << endl)

回答4:

Alternative:

struct myclass { 
    int i;
    inline operator int() const 
    {
        return i; 
    }
};