std::function::operatorbool (3) Linux Manual Page

std::function<R(Args…)>::operatorbool – std::function<R(Args…)>::operatorbool

Synopsis

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!