Re: ? Function Pointer to a Method of Unknown Class

"Igor Tandetnik" <>
Sat, 16 Sep 2006 08:08:46 -0400
"Alec S." <@> wrote in message

I've got a class which needs to store a pointer to a function. The
class will use that as a callback to pass some data to the specified
function when the data changes.

I need to be able to pass a method of the required format from an
unknown class to it.

For example:

typedef void(*Z)(int);
class A {
   int i;
   Z fp;
   void ReadI();
class B {
   void init();
   void Foo(int t=0;);
   A m_a;

void B::init() {

Z is defined to be a plain non-member function. You are trying assign a
member function pointer to it. This is not going to work - mainly
because A does not know which object to call the member function on.

You can make B::Foo static, then the assignment will work. Of couse Foo
won't then be able to access B's data members. Alternatively, consider
something like this:

class ICallback {
    virtual void HaveI(int i) = 0;

class A {
    ICallback* callback;
    A(ICallback* ?) : callback(c) {}
    void ReadI() {int i = something(); callback->HaveI(i);}

class B : public ICallback {
    A m_a;
    B() : m_a(this) {}
    void HaveI(int i);

With best wishes,
    Igor Tandetnik

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