?
Solved

pointer to function

Posted on 1999-01-26
5
Medium Priority
?
198 Views
Last Modified: 2010-04-02
I have a .h file:

typedef int (*funcptr)();
int f1();
class CSampleClass
{
public:
      funcptr p;
      CSampleClass();
      int f2();
};

In my .cpp file, it is OK for
{
...
CSampleClass a;
a.p=f1;
...
}

But when I have
{
      ...
CSampleClass a;
a.p=a.f2; //I need this.
...
}
it gives me an error:
'=' : cannot convert from 'int (CSampleClass::*)(void)' to 'int (__cdecl *)(void)'

Please help me to solve this problem.
0
Comment
Question by:yingchunli
  • 3
  • 2
5 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 120 total points
ID: 1185177
What you need are member pointers, but they aren't too easy to handle. In your case,

typedef int (CSampleClass::*PSAMPLECLASS_F2)();

CSampleClass a
PSAMPECLASS_F2 pMethodF2 = &CSampleClass::f2;

Then, you can use it like this:
(a.*pMethodF2)();

I admit that this is quite cumbersome... ;-)
0
 
LVL 86

Expert Comment

by:jkr
ID: 1185178
Also, note that
typedef int (CSampleClass::*PSAMPLECLASS_F2)();
is applicable for every member to 'CSampleClass' that takes no arguments and returns 'int', so
int CSampleClass::AnotherFunction()
{
//...
}
PSAMPECLASS_F2 pMethodF2 = &CSampleClass::AnotherFunction;

is also legal...

Feel free to ask if you have additional questions on this...



0
 

Author Comment

by:yingchunli
ID: 1185179
Thank you jkr. Your solution works. Here I just wonder why you need the
class instance a:
(a.*pMethodF2)();
How pMethodF2 is related to the class instance.

Why *pMethodF2(); does not work?
0
 
LVL 86

Expert Comment

by:jkr
ID: 1185180
Method pointers work only with an existing instance of a class. This is because
1. they're not real pointers to code, but indices into an object's method table
2. methods are passed an additional, 'inivisible' arguments that represents 'this'. The code of a method is the same one for each object (same location in memory), but the data (i.e. member variables) is stored at different locations.
0
 

Author Comment

by:yingchunli
ID: 1185181
Thank you jkr.
0

Featured Post

VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

Question has a verified solution.

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

Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
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.
Suggested Courses

864 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