callbacks using function pointers

[drsantosh82]

Hi,

I am trying to implement a callback routine using function pointers.
Basically, I am trying to avoid tying my callback invoking member to a
particular class.

Let me explain my problem with an example. The code snippet below
should help in explaining my problem better.

class A
{
public:
A();
~A();
void func();
private:
int i;
};


A::A()
{
cerr<<" In the constructor of A"<<endl;
i= 100;
}

A::~A()
{

}

void A::func()
{
cout<<"Value of the attribute is "<<i<<endl;
}

class B
{
public:

template <class T>
void callAFunction(void (T::*ptr)());

};

template <class T>
void B::callAFunction(void (T::*ptr)())
{
T *obj = new T;
obj->*ptr();
}

int main()
{
B Bobj;
Bobj.callAFunction(&A::func);

return 0;
}

The callAFunction of class B is expected to call the function whose
pointer (function pointer) is passed to it as an argument, but the
defintion of the function should not be tied to Class A specific
function pointer. For some reason, the compiler cribs at the statement
"obj->*ptr();"

Can anybody point out the error in this code snippet?

 

[Victor Bazarov]

[..]
template <class T>
void B::callAFunction(void (T::*ptr)())
{
T *obj = new T;
obj->*ptr();

(obj->*ptr)();

} [..]

V

 

[BobR]

Victor Bazarov wrote in message ...

[..]
template <class T>
void B::callAFunction(void (T::*ptr)()){
T *obj = new T;
obj->*ptr();

(obj->*ptr)();

What do you think about adding:

delete obj;

} [..]

V

 

[Victor Bazarov]

Victor Bazarov wrote in message ...

[..]
template <class T>
void B::callAFunction(void (T::*ptr)()){
T *obj = new T;
obj->*ptr();

(obj->*ptr)();

What do you think about adding:

delete obj;

Without knowing what the member function does, I would
probably say that it won't hurt, perhaps, most likely.

Of course, if it's all the same, and the function behind
the 'ptr' does not try to retain the pointer to this object,
it might actually be easier to do

(T().*ptr)();

then, instead of those two lines.

} [..]

V