Re: Function-pointers and classes

[Christian Gyrling <d98chgy@stud.hh.se>]

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Thanx for the info. I solved my first problem like that but now I have another one.

Take a look at the following code.

My problem occured when I was about to create multiple threads in a class.

Because of the CreateThread/beginthread functions I must call them with a plain

static function. ( the Create function ) But I´d like for different functions to be called

each time I started a new thread. Like some kind of thread-launcher.

By always sending the instance as the parameter to the Create-function I could

get a hold of the correct instance of the class but I had to get the specific function

to call in the Create-function.

Aaaaa, I thought. I use a member-function-pointer (.* / ->*) but there was an compilation error.

Could it have something to do with the casting???

If I call a public function in the class from the Create function there is no complaint.

 

int    Create( void *ptr ){

   MyClass     *obj = (MyClass*)ptr;

 

    ptr->*func();        // Ok

 

    ptr->*MemberFunctionPointer();        // Compile Error

} 

 

class MyClass

{

   void    (MyClass::*MemberFunctionPointer)();

 

   void    func();

   

   void    start() {

        MemberFunctionPointer = func;

        CreateThread(.....,..., Create, this,....,.... );

    }

}

 

The red line has an error at compilation that says something like. "Evaluates to int"

 

Many Thanks

/Christian Gyrling

 

 

----- Original Message -----

From: Cosmin Halmagi

To: gameprogrammer@topica.com

Sent: Wednesday, March 14, 2001 1:09 AM

Subject: Re: Function-pointers and classes

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This is for you and the other person who needed help on this.

Function pointers and class member pointers are two different entities in c++ (because class members have to deal with polymorfism, etc...)

So you can't assign to a function pointer the adress of a class member but you can assign it to a class member pointer.

(note: member pointers automaticly deal with polymorfism)

It is defined as: type (classname::*pointername)(parameters);

You can use such a pointer using the ".*" and "->*" operators.

Example:

#include <iostream.h>

class c{
public:
 int(c::*xx)(); /* pointer to member*/
 c();
 int x();
 y();

 };

c::c(){}
int c::x()

{

 return -1;

}
c::y()

{

 xx=&c::x;
 return (this->*xx)();

}

void main()
{

 c cc;
 cout<<cc.y(); /*-1*/

}

 

Unfortunatly this things are often not known.

So c++ is great after all :)

-----Original Message-----
From: Christian Gyrling <d98chgy@stud.hh.se>
To: Game Programmers Mailing List <gameprogrammer@topica.com>
Date: Tuesday, March 06, 2001 12:43 PM
Subject: Function-pointers and classes

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Hello all

 

First of all I give credit to all those who are taking control

of this multi-programmer-game.

 

Next I have a problem similar to that oh Josiha Avery. The thing is

how to use a function-pointer to an instance in a class.

 

int CacheSocket::create()

{

// Locally defined function pointer

// This is how the function-pointer should look to be accepted in the CreateThread

DWORD   (__stdcall *func)(void*);

 

// A function defined in the class we are currently in
func = this->ServerThread;            // THIS IS WHERE THE ERROR OCCURS

ERROR MSG

cannot convert from 'unsigned long (__stdcall CacheSocket::*)(void *)'

to 'unsigned long (__stdcall *)(void *)'

 

// Create the thread

CreateThread( NULL, 0, (LPTHREAD_START_ROUTINE)func, NULL, NULL, &ThreadId );

}

 

DWORD WINAPI CacheSocket::ServerThread( LPVOID lpParameter )

{

}

 

Please help me with this one

 

Christian Gyrling

 

 

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