Re: How to invoke the methods of an object selecting them from a table

From:

Stefano Sabatini <stefano.sabatini@caos.org>

Newsgroups:

comp.lang.c++

Date:

Tue, 5 Feb 2008 14:28:12 +0100 (CET)

Message-ID:

<slrnfqgp4q.7d5.stefano.sabatini@geppetto.reilabs.com>

On 2008-02-05, Sam <sam@email-scan.com> wrote:

Stefano Sabatini writes:

This is my solution for subject:

#include <string>
#include <iostream>

using namespace std;

class DumbThing {
public:
    void sayFoo() { cout << "Foo!" << endl; }

    static void sayFoo(DumbThing &t) {
        t.sayFoo();
    }

    void sayBar() { cout << "Bar!" << endl; }

    static void sayBar(DumbThing &t) {
        t.sayBar();
    }
};

struct ClassMethod {
    string name;
    void (*method)(DumbThing &);
};

int main(void) {

    struct ClassMethod DumbThingMethods[] = {
        { "sayFoo", &DumbThing::sayFoo },
        { "sayBar", &DumbThing::sayBar }
    };

    int DumbThingMethodsNum = sizeof(DumbThingMethods) / sizeof(ClassMethod);

    DumbThing t;
    for (int i=0; i < DumbThingMethodsNum; i++)
        DumbThingMethods[i].method(t);

    return 0;
}

The problem with this solution is that I have to create for each
method a corresponding static function, can you contrive a solution
which doesn't require this?

Many thanks in advance for any advice.

You want to use class member pointers:

// Declare:

class Foo {

public:
    void x();
    void y();
};

// Don't use arrays, when you really want a map:

std::map<std::string, void (Foo::*)() > methods;

// Initialize:

methods["x"]= &Foo:x;
methods["y"]= &Foo:y;

// Invoke some method on an object.

void callFoo(Foo *obj, std::string methodname)
{
   std::map<std::string, void (Foo::*)() >::iterator p=
    methods.find(methodname);

  if (p == methods.end())
     throw "You are a bozo";

  (obj->*(p->second))();
}

Hi Ondra and Sam, yes I finally got in touch with the
member pointers feature of C++, thank you so much for your hints and
explanations!! :-)

I already posted a solution using the memeber pointers, well now I see
I should rather use std::map rather than a plain array.

Best regards.
--
Stefano Sabatini
Linux user number 337176 (see http://counter.li.org)