Re: pointer to any member function of any class

Subject: pointer to any member function of any class.

The "C++ FAQ Lite" explains how to hand a pointer to a member function
to a signal handler etc, but only to a static function (33.2), to
a fixed class (33.2), any member of a fixed class (33.6), to a fixed
function of any object (functiods, 33.10).

What I wanted was to be able to hand any member function of any
created object to a signal hander etc.

The code below achieves this, using functiods and templates. The code
compiles cleanly with "g++ -Wall -pedantic" (g++ 4.0 & 4.1), haven't
tried other compilers.

#include <iostream>
using namespace std;

//The base-class of the functiod:
class callbase{
public:
 virtual ~callbase(){};
 virtual int operator() (int i)=0; //Change/add arguments to taste
};

template<class classtocall>
class calltemplate:public callbase{
 classtocall &object;
 int (classtocall::*methodtocall)(int);
public:
 calltemplate(classtocall &o,int (classtocall::*m)(int))
 : object(o){
   methodtocall=m;
 }
 int operator()(int i){ //Change/add arguments to taste
   return (object.*methodtocall)(i);
 }
};

//the signal handler, system call that starts a thread, etc:
class handler {
 callbase *m;
public:
 handler(callbase *b):m(b){};
 int h(int i){
   return (*m)(i); //Change/add arguments to taste
 }
};

// A class whose memebers we want to pass to a signal handler etc.
class worker {
 int i; //data member, just to show each instance is different
public:
 worker(int j):i(j){}
 int callme(int j){ //Change/add arguments to taste
   return j*i;
 }
 int pleasecall(int j){
   return j+i;
 }
};

//need a typedef for each class whose members we want to be called
typedef calltemplate<worker> call_worker;

int main (){
 worker w1(3);
 worker w2(7);
 handler h1(new call_worker(w1, &worker::pleasecall));
 handler h2(new call_worker(w2, &worker::callme));

 callbase *members[]={
   new call_worker(w1, &worker::callme),
   new call_worker(w2, &worker::pleasecall)};
 cout<<"h1 met arg 4="<<h1.h(4)<<endl;
 cout<<"h2 met arg 4="<<h2.h(4)<<endl;
 cout<<"arraymember: "<<(*members[0])(3)<<endl;;
 cout<<"arraymember: "<<(*members[1])(3)<<endl;;
}