Simple use of pointers to member functions

memfn.cc

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

using namespace std;

struct O
{
    void m(int n) const
    {
        cout << n << "\n";
    }

    void minus_one(int n) const 
    {
        cout << n-1 << "\n";
    }
};


// This function takes an object of type O and a pointer to
// one of its methods, and calls the method on the object.
void f(const O &o, void (O::*action)(int) const, int n)
{
    // Maybe do a bunch of stuff...
    
    (o .* action)(n);

    // More stuff...
}     



int main()
{
    O o;

    // Cause 0 to be printed by binding m to o with the .* ("dot star") operator.
    (o .* &O::m)(0);

    // Cause 1 to be printed by using mem_fun to create and object that calls O::m
    // (via its pointer) using an object of type O and an argument.
    mem_fun(&O::m)(&o, 1);

    // Cause 42 to be printed 16 times using the for_each algorithm, and O::m bound
    // to o.
    vector<int> c(16, 42);
    for_each(c.begin(), c.end(), bind1st(mem_fun(&O::m), &o));

    // Call o's method m to print 100.
    // This is equivalent to o.m(100), except that in practice, 
    // f will be doing more than just calling the method on the 
    // object.
    f(o, &O::m, 100);

    // Call o's method minus_one to print 99.
    // This is equivalent to o.minus_one(100), with the same caveats
    // as above.
    f(o, &O::minus_one, 100);
 

    return 0;
}