How to use std::function<> In C++
In C++ 11, there is a std::function<> template class that allows to pass functions as objects. An object of std::function<> can be created as follows.
std::function<return_type(arg1_type, arg2-type...)> obj_name // This object can be use to call the function as below return_type catch_variable = obj_name(arg1, arg2);
Example:
C++
// C++ program to demonstrate the passing // of functions as an object parameter #include <functional> #include <iostream> using namespace std; // Define add and multiply to // return respective values int add( int x, int y) { return x + y; } int multiply( int x, int y) { return x * y; } // Function that accepts an object of // type std::function<> as a parameter // as well int invoke( int x, int y, function< int ( int , int )> func) { return func(x, y); } // Driver code int main() { // Pass the required function as // parameter using its name cout << "Addition of 20 and 10 is " ; cout << invoke(20, 10, &add) << '\n' ; cout << "Multiplication of 20" << " and 10 is " ; cout << invoke(20, 10, &multiply) << '\n' ; return 0; } |
Addition of 20 and 10 is 30 Multiplication of 20 and 10 is 200
Passing a Function as a Parameter in C++
A function is a set of statements that take inputs, perform some specific computation, and produce output. The idea to use functions is to perform some commonly or repeatedly done tasks together and make a function so that instead of writing the same code again and again for different inputs.
The general form of a function is in the below format:
return_type function_name([ arg1_type arg1_name, ... ]) { // Perform Operations }
Passing a function as an argument is a useful concept in C++. This concept has already been used while passing a custom comparator function as an argument in std::sort() to sort a sequence of objects as per the need. In this article, we will discuss different ways to design functions that accept another function as an argument.
A function can be passed as a parameter with 3 approaches i.e.
- Passing as Pointer
- Using std::function<>
- Using Lambdas
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