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Problem with threads

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Started by brechtjah November 10, 2008 04:53 AM

8 comments, last by brechtjah 15 years, 5 months ago

brechtjah

122

Author

November 10, 2008 04:53 AM

Little background: I've just started win32, but need to get a function running in another thread to keep my UI untouched. The function looks something like:

void threadje( void *arg)
{
    SetDlgItemInt(hwnd, ID_stcSleep, 10, false);
    Sleep(1000);
}

I call this function in my WinMain function:

_beginthread(threadje, 0, (void*)hwnd);

I've been reading up on threads, however, it is quite hard to find some nice tutorials on what I want. I read somewhere that they just take void * as parameter, and I've copied most of the code found here from a site about threads (http://www.codeproject.com/KB/threads/MultithreadingTutorial.aspx). The error I'm getting is hwnd still being undeclared, I do not understand this as I'm giving it as an argument with the function. Any help would be very well appreciated, thank you

Googol PL3X

100

November 10, 2008 05:04 AM

Just because you are passing it doesn't mean that it exists. Make sure that there is something like this somewhere in your code:

HWND hWnd = NULL;

if there isn't, add it in your global variable declarations.

OldProgie2

158

November 10, 2008 05:07 AM

Although you are passing hwnd into your thread, you are not actually using it.
You need to use arg and cast it to the required type, as follows

void threadje( void *arg){    if ( 0 != arg )    {        HWND* hwnd = (HWND *)arg;        SetDlgItemInt(hwnd, ID_stcSleep, 10, false);    }    Sleep(1000);}

OldProgie2

158

November 10, 2008 05:09 AM

Quote:Original post by Googol PL3X
Just because you are passing it doesn't mean that it exists. Make sure that there is something like this somewhere in your code:

HWND hWnd = NULL;

if there isn't, add it in your global variable declarations.

I wouldn't use it as a global. The function may be used by multiple windows, in which case, each process would be picking up the same (wrong) window handle.

brechtjah

122

Author

November 10, 2008 05:14 AM

Thanks for the quick reactions...
Unfortunately, your code did not work, Googol PL3X.

By using the code of OldProgie2 I'm getting this error:
cannot convert `HWND__**' to `HWND__*' for argument `1' to `BOOL SetDlgItemInt(HWND__*, int, UINT, BOOL)'

zdlr

266

November 10, 2008 05:17 AM

HWND* hwnd = (HWND *)arg;

becomes

HWND hwnd = (HWND)arg;

?

OldProgie2

158

November 10, 2008 05:18 AM

Quote:Original post by brechtjah
Thanks for the quick reactions...
Unfortunately, your code did not work, Googol PL3X.

By using the code of OldProgie2 I'm getting this error:
cannot convert `HWND__**' to `HWND__*' for argument `1' to `BOOL SetDlgItemInt(HWND__*, int, UINT, BOOL)'

Sorry, forgot HWND is alread a pointer.

Try

HWND hwnd = (HWND)arg;

brechtjah

122

Author

November 10, 2008 05:23 AM

void  threadje( void *arg){    while(true) {    HWND hwnd = (HWND)arg;    SetDlgItemInt(hwnd, ID_stcSleep, class.getPlayTime() , false);    Sleep(1000);    }}

Thank you all very much, it works very well now, however, if I may, can I ask why you have to cast it : - )
Since I'm just learning ^^

Thanks

zdlr

266

November 10, 2008 05:40 AM

SetDlgItemInt expects a HWND__* and arg is just a void*. You might expect the compiler to just realise that pointers can be cast, but that wouldn't be typesafe - what if the arg that was passed in was a char*, for example?

brechtjah

122

Author

November 10, 2008 06:03 AM

Oh thanks, I think I get it

Problem with threads

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