std::function::operator bool

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

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

#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!

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
Relational operators
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Pairs and tuples
pair
tuple (C++11)
piecewise_construct_t (C++11)
piecewise_construct (C++11)
Swap, forward and move
swap
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
declval (C++11)

Member functions
function::function
function::~function
function::operator=
function::swap
function::assign
function::operator bool
function::operator()
function::target_type
function::target
Non-member functions
operator==operator!=
std::swap(std::function)
Helper classes
std::uses_allocator<std::function>

std::function::operator bool

Contents

[edit] Parameters

[edit] Return value

[edit] Exceptions

[edit] Example