Noob boost :: link function feedback function

Question

#include <boost/bind.hpp>
#include <iostream>

using namespace std;
using boost::bind;

class A {
public:
    void print(string &s) {
        cout << s.c_str() << endl;
    }
};


typedef void (*callback)();

class B {
public:
    void set_callback(callback cb) {
        m_cb = cb;
    }

    void do_callback() {
        m_cb();
    }

private:
    callback m_cb;
};

void main() {
    A a;
    B b;
    string s("message");
    b.set_callback(bind(A::print, &a, s));
    b.do_callback();

}

So what I'm trying to do is to disable the print message method of a stream when b the callback is activated. I get an unexpected number of arguments from msvc10. I'm sure this is a super noob basic, and I'm sorry in advance.

Answer 1

replace typedef void (*callback)();withtypedef boost::function<void()> callback;

A linked function does not create a regular function, so you cannot just store it in a regular function pointer. However, it boost::functioncan handle anything if it is allowed with the correct signature, so you want to. It will work with a function pointer or functor created with a binding.

:

#include <boost/bind.hpp>
#include <boost/function.hpp>
#include <iostream>

// i prefer explicit namespaces, but that a matter of preference

class A {
public:
    // prefer const refs to regular refs unless you need to modify the argument!
    void print(const std::string &s) {
        // no need for .c_str() here, cout knows how to output a std::string just fine :-)
        std::cout << s << std::endl;
    }
};


// holds any arity 0 callable "thing" which returns void
typedef boost::function<void()> callback;

class B {
public:
    void set_callback(callback cb) {
        m_cb = cb;
    }

    void do_callback() {
        m_cb();
    }

private:
    callback m_cb;
};

void regular_function() {
    std::cout << "regular!" << std::endl;
}

// the return type for main is int, never anything else
// however, in c++, you may omit the "return 0;" from main (and only main)
// which will have the same effect as if you had a "return 0;" as the last line
// of main
int main() {
    A a;
    B b;
    std::string s("message");

    // you forget the "&" here before A::print!
    b.set_callback(boost::bind(&A::print, &a, s));
    b.do_callback();

    // this will work for regular function pointers too, yay!
    b.set_callback(regular_function);
    b.do_callback();

}