c++ convert class to boolean

Question

With all of the fundamental types of C++, one can simply query:

if(varname)

and the type is converted to a boolean for evaluation. Is there

Answer 1

Simply implement operator bool() for your class.

e.g.

class Foo
{
public:
    Foo(int x) : m_x(x) { }
    operator bool() const { return (0 != m_x); }
private:
    int m_x;
}

Foo a(1);
if (a) { // evaluates true
    // ...
}

Foo b(-1);
if (b) { // evaluates true
    // ...
}

Foo c(0);
if (c) { // evaluates false
    // ...
}