使用Boost.Bind打印矢量元素

Question

I need to print the values inserted in the vector using Boost.Bind. Please find the code snippet below:

Please let me know what I am missing here?

   class Test
    {
        int i;

    public: 
        Test() {}

        Test(int _i)
        {
            i = _i;
        }

        void print()
        {
            cout << i << ",";
        }
    };


    int main()
    {
        std::vector<Test> vTest;
        Test w1(5);
        Test w2(6);
        Test w3(7);
        vTest.push_back(w1);
        vTest.push_back(w2);
        vTest.push_back(w3);

        std::for_each(vTest.begin(), vTest.end(),boost::bind(boost::mem_fn(&Test::print), _1, ?)); // How do I print Vector elements here?

    }

Answer 1

Maybe you do not want to have the parameter i for your function print() ? If so, you should simply do like this:

std::for_each(vTest.begin(), vTest.end(),boost::bind(&Test::print, _1));

This will output something like this: 5,6,7, . See live .

If you still want to have some argument passed into your function, then you should pass it to bind() :

std::for_each(vTest.begin(), vTest.end(),boost::bind(&Test::print, _1, 0));

0 will be your argument for Test::print() . And, in case of your code, you will have next output: 0,0,0, . See live .

If you fix function to next one:

    void print(int i)
    {
        cout << this->i << " " << i << ",";
    }

output will be next: 5 0,6 0,7 0, . See live

Answer 2

You can do it without boost like this

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>

class Test {
    int i;
public: 
    Test() {

    }

    Test(int _i) {
        i = _i;
    }

    void print() const {
        std::cout << i << std::endl;
    }
};

int main() {
    std::vector<Test> vTest;
    Test w1(5);
    Test w2(6);
    Test w3(7);
    vTest.push_back(w1);
    vTest.push_back(w2);
    vTest.push_back(w3);
    // use lambda
    std::for_each(vTest.begin(), vTest.end(), [&](const Test& t){ t.print(); });
    // use std::bind
    std::for_each(vTest.begin(), vTest.end(), std::bind(&Test::print, std::placeholders::_1));
    return 0;
}

Answer 3

You don't need bind there. Just replace the for_each from your code with the below statement.

std::for_each(vTest.begin(), vTest.end(), std::mem_fn(&Test::print)) ;