C++ Functional Library - Operator Bool

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Description

It is used to check if a valid target is contained.

Declaration

Following is the declaration for std::function::function::operator bool.

 explicit operator bool() const; 

C++11

 explicit operator bool() const; 

Parameters

none

Return Value

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

Exceptions

noexcept: It doesnot throw any exceptions.

Example

In below example for std::function::operator bool.

 #include <functional> #include <iostream> void sampleFunction() { std::cout << "This is the sample example of function!\n"; } void checkFunc( std::function<void()> &func ) { if( func ) { std::cout << "Function is not empty! It is a calling function.\n"; func(); } else { std::cout << "Function is empty.\n"; } } int main() { std::function<void()> f1; std::function<void()> f2( sampleFunction ); std::cout << "f1: "; checkFunc( f1 ); std::cout << "f2: "; checkFunc( f2 ); } 

The output should be like this −

 f1: Function is empty. f2: Function is not empty! It is a calling function. This is the sample example of function!