CreateThread problem

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5 total messages Started by Christophe MINETTI Wed, 09 Jan 2008 08:58

#773

Author: Christophe MINETTI
Date: Wed, 09 Jan 2008 08:58

26 lines
1549 bytes

Hi all,

I have few problems with the CreateThread function. I am using a frame
grabber; to acquire an image I have to create a thread with the function
CreateThread. Here is my code :

threads_hdls[0] = CreateThread(NULL,0,GrabWithoutCallback,
&user_card[0], 0,NULL) ;

with the function :

DWORD WINAPI TFrameGrabber::GrabWithoutCallback(LPVOID _param)

When compiling, I have the following error messages :

Cannot convert unsigned long(stdcall*(_closure)(void*))(void *) to
unsigned long (__stdcall*)(void*)
Type mismatch in lpStartAdress in call to __stdcall
CreateThread(_Security_Attributes....)

I don't see where is the problem as the function GrabWithoutCallBack is
defined as requested by CreateThread ....

Many thanks in advance.

Christophe

Re: CreateThread problem

#774

Author: AlexB
Date: Wed, 09 Jan 2008 09:29

20 lines
1226 bytes

Christophe MINETTI wrote:

> I have few problems with the CreateThread function.
...
> threads_hdls[0] = CreateThread(NULL,0,GrabWithoutCallback,
> &user_card[0], 0,NULL) ;
... 
> DWORD WINAPI TFrameGrabber::GrabWithoutCallback(LPVOID _param)

Declare this metod as static:

class TFrameGrabber
{
 ...
 static DWORD WINAPI GrabWithoutCallback(LPVOID _param);
 ...
}

-- 
Alex

Re: CreateThread problem

#776

Author: AlexB
Date: Wed, 09 Jan 2008 12:03

12 lines
1181 bytes

Christophe MINETTI wrote:

> It works fine !

But don't forget that static methods don't receive hidden 'this'
parameter. It means that inside method you can't use fields of class
directly (i.e. this->SomeField doesn't work); if you need pointer on
class instance you should pass it manually (for example via global
variable or as part of parameters ("LPVOID _param")).

--
Alex

Re: CreateThread problem

#775

Author: Christophe MINETTI
Date: Wed, 09 Jan 2008 12:44

28 lines
1467 bytes

Thanks Alex,

It works fine !

Christophe

AlexB wrote:

> Christophe MINETTI wrote:
>
> > I have few problems with the CreateThread function.
> ...
> > threads_hdls[0] = CreateThread(NULL,0,GrabWithoutCallback,
> > &user_card[0], 0,NULL) ;
> ...
> > DWORD WINAPI TFrameGrabber::GrabWithoutCallback(LPVOID _param)
>
> Declare this metod as static:
>
> class TFrameGrabber
> {
>  ...
>  static DWORD WINAPI GrabWithoutCallback(LPVOID _param);
>  ...
> }
>
> --
> Alex

Re: CreateThread problem

#777

Author: Christophe MINETTI
Date: Wed, 09 Jan 2008 13:09

20 lines
1395 bytes

I had noticed it.

Many thanks.

Christophe

AlexB wrote:

> Christophe MINETTI wrote:
>
> > It works fine !
>
> But don't forget that static methods don't receive hidden 'this'
> parameter. It means that inside method you can't use fields of class
> directly (i.e. this->SomeField doesn't work); if you need pointer on
> class instance you should pass it manually (for example via global
> variable or as part of parameters ("LPVOID _param")).
>
> --
> Alex

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