Operator overload c++

Question

I need to overload this operator (mainMenu is class type called 'Menu'):

if (mainMenu) {
    cout << "The mainMenu is valid and usable." << endl;
}

I tried this, but it didn't work:

bool operator!(const Menu& lobj);

Answer 1

In the condition of this if statement

if (mainMenu)

the logical negation operator ! is not used.

Instead you could write for example

if ( !!mainMenu )

However it is better to declare an explicit conversion operator like

explicit operator bool() const;

In this case you could write

if (mainMenu)

Here is a demonstrative program that shows a difference between these operators.

#include <iostream>

struct A
{
    bool operator !() const
    {
        return false;
    }

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

int main() 
{
    if ( !!A() ) std::cout << "Hello\n";

    if ( A() ) std::cout << "World!\n";

    return 0;
} 

The program output is

Hello
World!