Re: Timer Callback - C / C++ / MFC Discussion Boards

Kayembi6-Aug-03 5:27

6-Aug-03 5:27

Thanks. I guess I need to add lots of error-handling code to sort this out. I ought to get into good habits now, so thanks for the advice.
Cheers,
KB

Timer Callback

LittleYellowBird6-Aug-03 0:31

LittleYellowBird

6-Aug-03 0:31

Hi,

I'm trying to use a timer call back function but I can't get it to compile.

I set up the timer for a 1 second interval like this:-
m_uSampleTimerID = SetTimer( 1,1000,TimerTakeSample );

My function is declared like this:-
void CALLBACK EXPORT COxygraphView::TimerTakeSample(HWND hWnd, UINT nMsg, UINT nTimerID, DWORD dwTime)

BUT the SetTime command gives the following error:-
:\Oxygraph\OxygraphView.cpp(575) : error C2664: 'SetTimer' : cannot convert parameter 3 from 'void (struct HWND__ *,unsigned int,unsigned int,unsigned long)' to 'void (__stdcall *)(struct HWND__ *,unsigned int,unsigned int,unsigned l
ong)'

This is all in the View part of an MFC app. It doesn't seem to like the return type of the function.

Any ideas what's wrong with it?

Thanks

Ali

Re: Timer Callback

Member 4242596-Aug-03 0:41

Member 424259

6-Aug-03 0:41

Hey can i suggest u one thing..
Check out if u like this thing
instead of calling a call back function
just go to class wizard map the WM_TIMER for the view class
then call the set timer function with parameters(1000, timeasperuwant, NULL)
in this case the Functiopn mapped for WM_TIMER will be called..
please check out and let me know
bye

Thanx
TAKE CARE

Re: Timer Callback

Member 4242596-Aug-03 0:42

Member 424259

6-Aug-03 0:42

this thing will work if u calling the set timer function in the view class itself..

Thanx
TAKE CARE

Re: Timer Callback

LittleYellowBird6-Aug-03 1:12

LittleYellowBird

6-Aug-03 1:12

Thanks for the suggestion. In fact I have got my code working like that at the moment, but I have several timers and I wanted to assign each one its own handling function.

Thanks anyway Smile | :)

Ali

Re: Timer Callback

ivor bigun6-Aug-03 0:58

ivor bigun

6-Aug-03 0:58

The problem is with the declaration of your TimerTakeSample function. I think its probably got something to do with that EXPORT (try removing it?) because the CALLBACK simply defines the function type as an _stdcall* and so that should compile.

Re: Timer Callback

LittleYellowBird6-Aug-03 1:09

LittleYellowBird

6-Aug-03 1:09

Thanks for the suggestion, I've tried it but the compiler still doesn't want to know (still the same error message).

Thanks anyway Smile | :)

Ali

Re: Timer Callback

ivor bigun6-Aug-03 1:08

ivor bigun

6-Aug-03 1:08

The actual problem is that the compiler is expecting a void (_stdcall*) (arglist...)function and your function has somehow been defined as a mere void (arglist...) function hence the error. Since the CALLBACK statement defines the (_stdcall*) you should not be having this issue, unless the EXPORT statement is doing something dopy (so try removing it), or the TimerTakeSample referred to in the SetTimer function is being linked to a different function? try specifying COxygraphView::TimerTakeSample(blah...) in your SetTimer function to make sure your linkage is correct (can't tell from your example where the SetTimer is being called from). I'm sure the answer will reveal itself Smile | :)

Re: Timer Callback

Ryan Binns6-Aug-03 1:11

Ryan Binns

6-Aug-03 1:11

The function must be declared as static

Hope this helps,

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Re: Timer Callback

ivor bigun6-Aug-03 1:31

ivor bigun

6-Aug-03 1:31

Haha, yes the declaration should be static void CALLBACK etc. well done ryan Smile | :)

Re: Timer Callback

Phil Speller6-Aug-03 1:53

Phil Speller

6-Aug-03 1:53

To expand on Ryan's post - it's all to do with pointers to member functions. Take a look at this[^] site - it will explain all!

Phil

Re: Timer Callback

LittleYellowBird6-Aug-03 2:09

LittleYellowBird

6-Aug-03 2:09

Thanks, the link looks really helpful, looks like I need to do some reading!

Smile | :)

Ali

Re: Timer Callback

LittleYellowBird6-Aug-03 2:12

LittleYellowBird

6-Aug-03 2:12

You're right changing the funstionto static gets rid of the compiler error. However, now I have more errors calling functions from the timer function. Looks like I need to read up on static functions!

Thanks for the help, much appreciated Smile | :)

Ali

Re: Timer Callback

Ryan Binns6-Aug-03 2:19

Ryan Binns

6-Aug-03 2:19

You're welcome Smile | :)

Alison Pentland wrote:
However, now I have more errors calling functions from the timer function. Looks like I need to read up on static functions!

Good idea Wink | ;)

Your errors at the moment are probably because you're calling non-static members from your static function. You can't do that Smile | :)

. The general way of using static functions as callbacks is to pass a pointer to the object as the lParam value that gets passed to the callback function, and then using that pointer to access the other class members.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Re: Timer Callback

Phil Speller6-Aug-03 3:04

Phil Speller

6-Aug-03 3:04

Declaring a member function of class as static will remove the need for an instance of the class to be associated with it - i.e. no this pointer. What this means is that it can't access any of the normal member functions/variables - precisely because there is no associated this pointer. However, supply the static function with a pointer to an instance of the class and you can access all functions/variables (even private ones) via that pointer - because the static function is still declared in the scope of the class.

In terms of pointers to functions, because a static member function has no associated this pointer you can obtain it's address directly (just like a C function) - this is why Ryan's suggestion worked. Any normal member function must have an associated this pointer with it, so even when you take the address of a member function you must still use it with a pointer to an instance of the class as well.

class CMyClass<br />
{<br />
public:<br />
  void MyFn (void);<br />
  static void MyStaticFn (CMyClass *);<br />
};<br />
<br />
typedef void(* FnPtr)(CMyClass*);  // C style fn pointer<br />
typedef void(CMyClass::* MemberFnPtr)();  // C++ style fn pointer<br />
<br />
CMyClass* pMyClass = new CMyClass;<br />
<br />
MemberFnPtr pMFn = &CMyClass::MyFn;<br />
pMyClass->MyFn();           // Calling as normal<br />
pMyClass->*pMFn();          // Calling via pointer to member fn<br />
<br />
FnPtr pFn = &CMyClass::MyStaticFn;<br />
(*pFn)( pMyClass );         // Calling static member fn

[edit]
You could try using the nIDEvent parameter of SetTimer to hold the pointer to your class instance - cast it back to the correct type and use within your static fn.
[/edit]

Hope this helps,

Phil

Re: Timer Callback

Vitali Halershtein6-Aug-03 2:49

Vitali Halershtein

6-Aug-03 2:49

Hi Alison,

I am not sure that "static" is right method. See following:
The citation:

-The lpfnTimer callback function need not be named TimerProc, but it must be defined as follows:

-void CALLBACK EXPORT TimerProc(
- HWND hWnd, // handle of CWnd that called SetTimer
- UINT nMsg, // WM_TIMER
- UINT nIDEvent // timer identification
- DWORD dwTime // system time
-);

So, TimerProc should be a function insted class method.

Re: Timer Callback

Ryan Binns6-Aug-03 4:19

Ryan Binns

6-Aug-03 4:19

Talik wrote:
So, TimerProc should be a function insted class method.

There is nothing wrong with using a static member. The compiler treats functions and static members in exactly the same way.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Reselect on combo box OnDropdown

paulccc5-Aug-03 23:58

paulccc

5-Aug-03 23:58

Hi everyone,

Having a nightmare problem - hoping someone can help!

When I catch OnDropdown for a combo box and try programmatically selecting an item different than the current selection the control reselects a different item!

I have a list box, let's say it's got these items:

_________________
| Paul Maddox
| Paul Mdx
| Paul
|_________________

If "Paul Mdx" was selected last time, when I open the dropdown I want it to select "Paul".

So, I've hooked the OnDropdownMyCombo function and done:

m_combo.SetCurSel(m_combo.FindExactMatch(-1,"Paul"));

After the selection I do GetCurSel and GetLBText to double-check the correct selection is made, which it is.

However, the control will show "Paul Maddox" as being selected in the dropped down list, BUT "Paul" shown in the edit box.

If anyone has come across this or has any suggestions, I'm more than open to hear them!

Many thanks,
Paul.

Re: Reselect on combo box OnDropdown

HPSI6-Aug-03 2:44

HPSI

6-Aug-03 2:44

The framework sets the new selection after OnDropdownMyCombo is called, so your code has no effect. Your code would work if you put it in the ON_CBN_SELCHANGE handler.

HPS HwndSpy - GUI developer's aid to visually
locate and inspect windows. For the month of August
only, use coupon code CP-81239 for 30% off.

Printing How?

wow99995-Aug-03 23:42

wow9999

5-Aug-03 23:42

Hi all
I create a file by using CStdioFile.
I want to sent this file to Printer, which function should i use?

Thanks

Re: Printing How?

HPSI6-Aug-03 2:21

HPSI

6-Aug-03 2:21

Use ShellExecute()
```
ShellExecute(m_hWnd, "print", "MyFile.txt", NULL, NULL, SW_HIDE);
```
This will execute the program associated with the .txt extension and tell it to print the file.

Use system()
```
system("copy "MyFile.txt" lpt1:");
```
This will send the file to the printer using the DOS copy command. Note that the last (partial) page will probably not be printed, unless you send a formfeed.

Use MFC's doc/view printing architecture. See the Printing section here on CP for more details.

HPS HwndSpy - GUI developer's aid to visually
locate and inspect windows. For the month of August
only, use coupon code CP-81239 for 30% off.

vfw depression

mr pier5-Aug-03 23:37

mr pier

5-Aug-03 23:37

hello world,
I develop video capture application, and i need to extract frames as bmp.

I use directshow to capture my 1394 dv, and vfw.h to extract frames.

capture is ok and works quitte well.

But (terrific 'but'!!)

when i try to use vfw.h functions, compilation gives no error, but i always have the sam linking errors
error LNK2001: unresolved external symbol _AVIFileInit@0

I tried everything, vfw32.lib seems to be the same version, it describes the same functions...

My project is not a commercial one, it has artistic purposes. Deadlines are getting closer and i am afraid to be late.

PLEASE HELP

Mr PIER

Re: vfw depression

HPSI6-Aug-03 1:48

HPSI

6-Aug-03 1:48

Go to Project | Settings | Link | Object/library modules, and add Vfw32.lib.

HPS HwndSpy - GUI developer's aid to visually
locate and inspect windows. For the month of August
only, use coupon code CP-81239 for 30% off.

Re: vfw depression

Anonymous8-Aug-03 8:52

Anonymous

8-Aug-03 8:52

thanks
it helped,

but i can't launch AVIStreamOpenFromFile even if i close the directshow's capture graph, i don't understand why

any idea ??

Webbrowser::Newwindow() Problem!!

xxhimanshu5-Aug-03 23:22

xxhimanshu

5-Aug-03 23:22

Hi All,
I Want to use the newwindow event to not open the new window and open the
same link in parent window...I have declared the function like this..
DISP_FUNCTION_ID(CWebBrowser2, "NewWindow2",DISPID_NEWWINDOW2, OnNewWindow,
VT_EMPTY, VTS_BSTR VTS_I4 VTS_BSTR VTS_PVARIANT VTS_BSTR VTS_PBOOL)
and the function definition says..
void CBrowser::OnNewWindow(BSTR URL, long Flags, BSTR TargetFrameName,
VARIANT* PostData, BSTR Headers, BOOL FAR* Cancel)
{
if (m_pBrowserApp) {
COleVariant varEmpty;
if (Cancel != NULL )
*Cancel = TRUE;
m_pBrowserApp->Navigate(URL, &varEmpty, &varEmpty, &varEmpty, &varEmpty);
}
}
MSDN says it should work like this only..but unfortunately this is not
working for me..Pls helpAny help or pointers are higly appreciated..Thanks a
lot in advance..

Himanshu

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