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std::function::operator bool

From cppreference.com
< cpp‎ | utility‎ | functional‎ | function
 
 
 
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explicit operator bool() const;
(since C++11)

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

Contents

[edit] Parameters

(none)

[edit] Return value

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

[edit] Exceptions

noexcept specification:  
noexcept
  

[edit] Example

#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!