Function Pointers

[Egz0N]

i like it marwex .. +rep

[marwex89]

I appreciate it, egzon Thanks

Posted via CodeCall Mobile

[Talo]

You explained it great, but I still can't get my head around it to be honest. Well everybody says it's a difficult subject i'll re-read it later today and try again.

Thanks for making this tutorial marwex89 .

[marwex89]

Thanks, Talo (and Welcome to CodeCall )... Have a coffee and re-read it, make some small example programs, and you'll soon get the hang of it

[satishkumar432]

Hello Marwex89,

Thnx for posting very useful document on function pointers. This post is pretty much helpful to novice programmers like me in C++ to understand these fuzzy concepts. But I still have a small doubt regarding it.

Please refer to the below code. In the below code Im trying to access the function pointer initialized in the constructor, but the first statement((b1.*fptr)() always throws a compilation error, but the with the statement (b1.*(b1.fptr))()) the code works as expected.

#include<iostream>
using namespace std;
class base
{
 public:
 void(base::*fptr)(void);
 void func(void)
 {
  cout<<"Hello im in func"<<endl;
  }
  base()
  {
  fptr=&base::func;
  }
};
int main()
{
base b1;
(b1.*fptr)();//Compilation Error as "fptr undelcared"
(b1.*(b1.fptr))()) //works perfectly fine.
return 0;
}

Clarification in this regard is very much appreciated.

[marwex89]

Hello Marwex89,

Thnx for posting very useful document on function pointers. This post is pretty much helpful to novice programmers like me in C++ to understand these fuzzy concepts. But I still have a small doubt regarding it.

Please refer to the below code. In the below code Im trying to access the function pointer initialized in the constructor, but the first statement((b1.*fptr)() always throws a compilation error, but the with the statement (b1.*(b1.fptr))()) the code works as expected.

#include<iostream>
using namespace std;
class base
{
public:
void(base::*fptr)(void);
void func(void)
{
cout<<"Hello im in func"<<endl;
}
base()
{
fptr=&base::func;
}
};
int main()
{
base b1;
(b1.*fptr)();//Compilation Error as "fptr undelcared"
(b1.*(b1.fptr))()) //works perfectly fine.
return 0;
}

Clarification in this regard is very much appreciated.

Note: Use the code tags (# button) when posting code

This makes sense because the compiler thinks fptr is a variable when you call it this way:

(b1.*fptr)();

It wants to see

base b1;
    
void(base::*fptr)(void);
fptr = &base::func;
(b1.*fptr)();

Which actually works.

While when you type *(b1.fptr) you dereference the value that b1.fptr returns, i.e. your member function pointer.

Welcome to CC and feel free to ask if you have more questions.

[satishkumar432]

Thank you marwex89 for a quick reply ....But still a doubt creeps in my mind please bear me....

base b1;

void(base::*fptr)(void);
fptr = &base::func; ..........Why do we need to initialize it again when we have already done it in the constructor.
(b1.*fptr)();

[marwex89]

Ah, you didn't quite get the point... This fptr is NOT the same as your class member! It is a separate local variable in your main function. You could rename it to e.g. "my_variable" and it would still work. For using the member variable you can do (as you wrote)

(b1.*(b1.fptr))();

[satishkumar432]

Thanks again....got it.