Solved

pointer to member function

Posted on 1998-10-21
6
203 Views
Last Modified: 2010-04-02
I am trying to create a function pointer in my class
that will point to different member function within the
same class.

My problem is that I cant figure out how to call the
function pointer.

Here is a very simple example:

class CDevice
{
public:
      CDevice();
      typedef void (CDevice::* EraseFnPtr)(int i);
      EraseFnPtr Erase;

      void Erase1(int i);
      void Erase2(int i);
};

CDevice::CDevice()
{
      Erase = &CDevice::Erase1;
}

void CDevice::Erase1(int i)
{
      printf("Erase1 %d\n",i);
}


void main()
{
      CDevice Device;
      (Device.*Erase)(34);
}

I want the program to print out "Erase1 34".

But I get 2 compile errors that say
error C2065: 'Erase' : undeclared identifier
error C2297: '.*' : bad right operand

both regarding to this line:
----->      (Device.*Erase)(34);
This is in Visual C++ 5.0

So How do I call the Erase function pointer?
thanks

PS I dont want to change the way the class is set up, In other words I want the function pointer to be within the CDevice class.

0
Comment
Question by:vinny5
  • 5
6 Comments
 
LVL 22

Accepted Solution

by:
nietod earned 170 total points
ID: 1175717
Problem: erase is a member.
0
 
LVL 22

Expert Comment

by:nietod
ID: 1175718
In

(Device.*Erase)(34);

the compiler is looking for a local or global variable called "Erase".  But there is none.  The erase you want is a member of the class try

(Device.*Defice.Erase)(34);

Or better yet, define a member function that does the calling using the pointer.  Then call that member function here.  That hides the pointer-to-member stuff inside the class.   (Where I would say it belongs.  In most cases, I think I would make it entirely private to the class.)

Let me know if you have questions.
0
 
LVL 22

Expert Comment

by:nietod
ID: 1175719
Wait a second.

>> PS I dont want to change the way the class is set up, In other words
>> I want the function pointer to be within the CDevice class

You don't want it to be within the class?  but you declared it there!  You can declare it outside the class, if that is what you want.   (But I wouldn't recommend it.)  I would move the typedef outside as well, in that case.
0
Optimizing Cloud Backup for Low Bandwidth

With cloud storage prices going down a growing number of SMBs start to use it for backup storage. Unfortunately, business data volume rarely fits the average Internet speed. This article provides an overview of main Internet speed challenges and reveals backup best practices.

 
LVL 22

Expert Comment

by:nietod
ID: 1175720
Opps, ignore that last comment.  In my mind I added a "don't" that wasn't there.
0
 

Author Comment

by:vinny5
ID: 1175721
BAM!

thanks neitod...
Im sorting of doing what you recommended I was just trying to create a simple
example to illustarte my question..  but  (Device.*Device.Erase)(34);
was exactly what I was looking for.

gracias

0
 
LVL 22

Expert Comment

by:nietod
ID: 1175722
de nada
0

Featured Post

Simplifying Server Workload Migrations

This use case outlines the migration challenges that organizations face and how the Acronis AnyData Engine supports physical-to-physical (P2P), physical-to-virtual (P2V), virtual to physical (V2P), and cross-virtual (V2V) migration scenarios to address these challenges.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

When writing generic code, using template meta-programming techniques, it is sometimes useful to know if a type is convertible to another type. A good example of when this might be is if you are writing diagnostic instrumentation for code to generat…
Container Orchestration platforms empower organizations to scale their apps at an exceptional rate. This is the reason numerous innovation-driven companies are moving apps to an appropriated datacenter wide platform that empowers them to scale at a …
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

810 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question