# std::function<R(Args...)>::operator bool

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< cpp‎ | utility‎ | functional‎ | function

explicit operator bool() const noexcept; |  | (since C++11)

Checks whether *this stores a callable function target, i.e. is not empty.

### Parameters

(none)

### Return value

true if *this stores a callable function target, false otherwise.

### Example

Run this code

    #include <functional>
    #include <iostream>

    void sampleFunction()
    {
        std::cout << "This is the sample function!\n";
    }

    void checkFunc( std::function<void()> &func )
    {
        // Use operator bool to determine if callable target is available.
        if( func )
        {
            std::cout << "Function is not empty! Calling function.\n";
            func();
        }
        else
        {
            std::cout << "Function is empty. Nothing to do.\n";
        }
    }

    int main()
    {
        std::function<void()> f1;
        std::function<void()> f2( sampleFunction );

        std::cout << "f1: ";
        checkFunc( f1 );

        std::cout << "f2: ";
        checkFunc( f2 );
    }

Output:

    f1: Function is empty. Nothing to do.
    f2: Function is not empty! Calling function.
    This is the sample function!

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