Question

I am trying to get a bool value out of user defined object.
For example with float or int I can do something like

float a = 3.5
if (a) doSomething();

I want my class to look like this:

class Socket {
...
...
};
...
Socket T;

if (!T) cout << "Error occured";
else {
   doStuff();
}

Of course I can define a function that returns bool (like bool isValid();) and call it directly, but I would like to know if it is possible.

Answer 1

In C++11, you can safely convert your type to a boolean value:

explicit operator bool() const {return isValid();}

If your compiler doesn’t support that, then you could write the same thing without explicit; however, that can be a bit dangerous because it enables implicit conversions to any numeric type. Instead, you could use a hack known as the safe bool idiom:

private:
    typedef void (Socket::*safe_bool)() const;
    void safe_true() const {}
public:
    operator safe_bool() const {return isValid() ? &Socket::safe_true : 0;}

This returns a pointer type which can’t be converted into anything except bool.