Pointers to Class Member Functions

I am working on a class that holds a vector of class member functions. While normal function pointers a quite easy to implement I have discovered that using pointers to member functions take a bit more thought.

My first attempt:

Code:

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typedef void *pData;
typedef void(*pFunction)(pData);
class MyClass1
{
public:
    MyClass1() { m_a = 5; m_b = 10; }
    ~MyClass1() { }
    void Go();
    static void f1(pData d) { std::cout<<"Member Function 1.  a = " <<static_cast<MyClass1*>(d)->m_a <<"\n"; }
    static void f2(pData d) { std::cout<<"Member Function 2.  b = " <<static_cast<MyClass1*>(d)->m_b <<"\n"; }
private:
    std::vector<pFunction> m_VecFunc;
    int                    m_a, m_b;
};
void MyClass1::Go()
{
    m_VecFunc.push_back(&f1);
    m_VecFunc.push_back(&f2) ;
    std::vector<pFunction>::iterator iter;
    for (iter = m_VecFunc.begin(); iter != m_VecFunc.end(); ++iter)
    {
        (*iter)(this);
    }
    return;
}

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This works quite well. The only problem is that in order to access member variables I have to pass this to the function and cast it to a MyClass1 pointer before each call to a member variable.
I'm not sure I like this. While it works it seems like more work than it should be, having to remember to cast each member variable before I use it.

So then I came up with my second approach.

Code:

---

class MyClass2
{
public:
    MyClass2() { m_a = 5; m_b = 10; }
    ~MyClass2() { }
    void f1() { std::cout<<"Member Function 1.  a = " <<m_a <<"\n"; }
    void f2() { std::cout<<"Member Function 2.  b = " <<m_b <<"\n"; }
    void Go();
    void DoCallBack(pFunction f, pData x) { f(x); }  // calls f(x)
private:
    static void call_f1(pData d) { static_cast<MyClass2*>(d)->f1(); }
    static void call_f2(pData d) { static_cast<MyClass2*>(d)->f2(); }
    int                    m_a, m_b;
    std::vector<pFunction> m_VecFunc;
};
void MyClass2::Go()
{
    m_VecFunc.push_back(call_f1);
    m_VecFunc.push_back(call_f2);
    std::vector<pFunction>::iterator iter;
    for (iter = m_VecFunc.begin(); iter != m_VecFunc.end(); ++iter)
    {
        (*iter)(this);
    }
    return;
}

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This also works quite well. I no longer have to cast each member variable before I can use it. The only problem now is that for each member function I want to take the address of, I have to have a second function just to call it. And I still have to pass this to the calling function.
I'm not sure I care for this either.

Is there a way of doing this so that I can directly use member variables without having to do any type casting?

For your examples you don't have to take the detour via a static function.

Code:

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#include <iostream>
#include <vector>

using namespace std;

class MyClass;

typedef void (MyClass::*pt2tMember)( int );

class MyClass {
public:
    MyClass() { m_a = 5; m_b = 10; m_c = 15; }

    ~MyClass() { }
    void Go();

    void f1( int d) {
        std::cout<<"Member Function 1.  a = " << m_a << "," << d <<"\n";
    }
    void f2( int  d) {
        std::cout<<"Member Function 2.  b = " << m_b << "," << d <<"\n";
    }
    void f3( int  d) {
        std::cout<<"Member Function 2.  c = " << m_c << "," << d <<"\n";
    }

private:
    std::vector< pt2tMember > m_VecFunc;
    int  m_a, m_b, m_c;
};

void MyClass::Go()
{
    m_VecFunc.push_back(&MyClass::f1);
    m_VecFunc.push_back(&MyClass::f2) ;
    m_VecFunc.push_back(&MyClass::f3) ;

    std::vector< pt2tMember >::iterator iter;
   
    int i = 0;
    for (iter = m_VecFunc.begin(); iter != m_VecFunc.end(); ++iter, ++i)
        (*this.*(*iter))( i );
    return;
}

int main() {
    MyClass a;
    a.Go();
}

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Kurt

What you wish you had is a "bound function pointer." It doesn't exist natively in C++, but you can implement it using tr1::binder objects. Other people have implemented equivalent mechanisms -- for instance, see:

http://www.tutok.sk/fastgl/callback.html

Quote:

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Originally Posted by ZuK

For your examples you don't have to take the detour via a static function.

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The impression that I got from everything that I read was that you could not take the address of a member function unless it was static. My very first attempt seemed to confirm this as I kept getting one error that I could not resolve. I never thought of calling the function pointer through this. That is exactly what I was looking for.... Thanks!

Quote:

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Originally Posted by ZuK

Code:

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(*this.*(*iter))( i );

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I think a better syntax is:

Code:

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(this->*iter)( i );

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They are equivalent, of course.

Quote:

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Originally Posted by brewbuck

Code:

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(this->*iter)( i );

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They are equivalent, of course.

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Code:

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error: no match for 'operator->*' in 'this ->* iter'

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this would work ( Calling member function pointers is a bit funny )

Code:

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(this->*(*iter))( i );

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Kurt

Quote:

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Originally Posted by ZuK

Code:

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error: no match for 'operator->*' in 'this ->* iter'

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this would work ( Calling member function pointers is a bit funny )

Code:

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(this->*(*iter))( i );

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Kurt

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Oops. I didn't read the code fully. Though iter was a bare member function pointer itself :)