Question

I have my class, where I overloaded the ! operator:

class obj
{
public:

    bool operator!() const
    { return this->str.length() == 0; }

private:

    string str;

};

With the ! operator i want to check the obj validity, so:

obj o;

// if o is not a valid object
if(!o)
   cerr << "Error";

Now I want to have the possibility to do this:

// if o is a valid object
if(o)
   cout << "OK";

How can I do?

Answer 1

Using C++11, you can do this by having an explicit operator bool:

explicit operator bool() const {
    return !!*this;
}

This operator is called if you ever need to cast your object to a bool explicitly (which is done by the if statement automatically). The implementation works by calling your operator ! on the receiver object, then returning the opposite result.

Hope this helps!