Re: pointer to any member function of any class
joosteto@gmail.com wrote:
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;;
}
My question would be, how does this accomplish "handing" *any* member
function of *any* class to a signal handler? I don't see any *signal*
handler, nor do I see any variation in the member functions. They
all take a single 'int' argument, they all return 'int', and they are
all non-cosnt. That's pretty far from "any" in my book.
Of course, it's possible that my terminology is simply different from
yours.
V
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