std::function::operator bool

From cppreference.com


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

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

#include <functional>
#include <iostream>
 
typedef std::function<void(int)> SomeVoidFunc;
 
class C {
  public:
    C(SomeVoidFunc void_func = nullptr)
        : void_func_(void_func)
    {
        if (!void_func_) {
            void_func_ = std::bind(&C::default_func, this, std::placeholders::_1);
        }
        void_func_(7);
    }
 
    void default_func(int i) { std::cout << i << '\n'; };
 
  private:
    SomeVoidFunc void_func_;
};
 
void user_func(int i)
{
    std::cout << (i + 1) << '\n';
}
 
int main()
{
    C c1;
    C c2(user_func);
}

Output:

7
8

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)

std::function::operator bool

Contents

[edit] Parameters

[edit] Return value

[edit] Exceptions

[edit] Example