std::bind with member function and this in c++

Question

I'm trying to learn C++ and I'm experimenting with the std::bind function of the standard library. As a result, I understood that std::bind allows to wrap a function and to partially apply the function. This works very well with functions that are not member functions of a class. Now I try to use std::bind with class member functions and the 'this' pointer but I can't compile and don't know how to fix this problem. Could someone help me to really understand std::bind ?

#include <iostream>
#include <functional>

class Class1 {
    public:
        Class1() = default;
        ~Class1() = default;
        void print(std::function<void(void)> function2) {
            function2();
        };
};

class Class2 {
    public:
        Class2() = default;
        ~Class2() = default;
        void test_bind() {
            std::function<void(void)> function2 = std::bind<void(void)>(&Class2::print, this);
            class1.print(function2);
        }
        void print() {
            std::cout << "CLASS 2" << std::endl;
        };

        Class1 class1;
};


int main(int ac, char **av)
{
    Class2 class2;

    class2.test_bind();
}

Don't use `bind`, use a lambda instead: `std::function function2 = [this](){ this->print(); }` — NathanOliver, Feb 23 '21 at 17:54
Yes sure but why i can't use std::bind in this case ? In which case is better to use lambda or std::bind ? — Progear, Feb 23 '21 at 17:55
@Progear You wrote `std::bind` which is wrong. Remove the `` part. — super, Feb 23 '21 at 17:57
General recommendation is to always use lambdas now. Lambdas can be optimized by the compiler in ways that std::bind cannot and lambdas can do everything std::bind can (in c++14 and higher). See [this](https://stackoverflow.com/questions/17363003/why-use-stdbind-over-lambdas-in-c14). — Dean Johnson, Feb 23 '21 at 17:58

score 2 · Accepted Answer · answered Feb 23 '21 at 18:03

Let the compiler deduce types based on passed arguments:

std::function<void(void)> function2 = std::bind(&Class2::print, this);

above is enough.

Version with explicit template arguments list looks like:

std::function<void(void)> function3 = std::bind<void(Class2::*)(),Class2*>(&Class2::print, this);

// std::bind<void(Class2::*)(),Class2*>
               / \           / \
                |             |---- pointer to type of object instance you invoke member function 
                |--- pointer to member function

Demo

Thank you it's much clearer now ! – Progear Feb 23 '21 at 18:07 — Progear, Feb 23 '21 at 18:07

std::bind with member function and this in c++

1 Answers1