std::function
It is function object with specific return type and a specific argument type and it is a generic, polymorphic function wrapper whose instances can store, copy, and call any target entity that can be called, in other word std::function can be used to store and call a function or function pointer or auto or return of lambda or return of bind().
In other word:
It is like “function pointer of C language“, we need to specify return type and parameter and then it will be used to call assigned function.
When will we use it (What is the Objective/purpose of std::function):
- If we want to assign the result of bind() or return of lambda to variable of specific type.
- When we want to pass the function logic as argument to algorithm (std::function is function object, we can pass this to algorithm ).
- std::function objects are useful for callback.
Header file:
#include<functional>
source code with example:
/*
Program: std::function
Author: Alpha Master
Date: 28 Feb 2021
*/
//Header File
#include<iostream>
#include<functional>
int add(int a, int b)
{ return a+b;}
int main()
{
std::cout<<"std::function"<<std::endl;
//Assign a function
std::function<int(int, int)>f1 = add;
//Assign a lambda
std::function<int(int, int)>f2 = [](int a, int b){ return (a+b);};
//Assign a bind call
std::function<int(int)>f3 = std::bind(add, 1, std::placeholders::_1);
//calling
std::cout<<"f1:"<<f1(1,2)<<std::endl;
std::cout<<"f2:"<<f2(1,2)<<std::endl;
std::cout<<"f3:"<<f3(2)<<std::endl;
return 0;
}
Output:
std::function f1:3 f2:3 f3:3