Problem splitting dynamically allocated CString - C / C++ / MFC Discussion Boards

Nemanja Trifunovic26-Jan-03 17:27

26-Jan-03 17:27

It would break a lot of existing code. This template class (which I need to reimplement) must have exactly the same interface as std::vector plus several extra functions.

Beer | [beer]

Changing screen saver programatically

Mahesh Perumal26-Jan-03 5:18

Mahesh Perumal

26-Jan-03 5:18

I want to change the screen saver without any message to user? Can u help me out?

Mahesh

Re: Changing screen saver programatically

Ken Mazaika26-Jan-03 11:56

Ken Mazaika

26-Jan-03 11:56

I've looked into this with no success....I'm not sure if it's possible....

Global memory (GlobalAlloc, etc...)

Dominik Reichl26-Jan-03 3:40

Dominik Reichl

26-Jan-03 3:40

Hello,

is the memory allocated by the GlobalAlloc function really global? Can different processes access the same memory block allocated by GlobalAlloc?

Thanks
-Dominik

Re: Global memory (GlobalAlloc, etc...)

Sigmund26-Jan-03 4:38

Sigmund

26-Jan-03 4:38

No. Memory allocated by GlobalAlloc is not visible to other process. If you want to share memory across process, i sugest that you use memory mapped files.

Also, MSDN state that GlobalAlloc is not the preferred way to allocate memory. Try the heap memory function instead (HeapAlloc, HeapFree, ect,ect).

Re: Global memory (GlobalAlloc, etc...)

Dominik Reichl26-Jan-03 6:03

Dominik Reichl

26-Jan-03 6:03

Ok, I will use memory mapped files.

Thank you!
-Dominik

Re: Global memory (GlobalAlloc, etc...)

Joe Woodbury26-Jan-03 21:37

Joe Woodbury

26-Jan-03 21:37

When you call ::CreateFileMapping with (HANDLE) LongToHandle(-1) as the first parameter, PAGE_READWRITE as the protection and a name, which is how other applications will access it by calling OpenFileMapping. If the creator will be in one set of permissions (like a service logged in as an administrator) and the other application will have lower permissions, you'll need to create and use SECURITY_ATTRIBUTES (you can create a NULL security attribute which essentially grants global rights to the memory.)

Problem splitting dynamically allocated CString

Wim Jans26-Jan-03 2:56

Wim Jans

26-Jan-03 2:56

Hi,

I have a problem splitting up a string.

I have a thread which will send a string to my main thread by posting a message.
I therefore create my string

<br />
CString *s = new CString();<br />
s->Format("%s#@@#%s", _T("Error"), _T("ErrorMessage"));<br />
PostMessage(UWM_SENDSTRING, (WPARAM)i, (LPARAM)s);<br />

The code is successfully received by my function.
However, here is where it goes wrong.

<br />
LRESULT CMyView::OnSendString(WPARAM wparam, LPARAM lparam)<br />
{<br />
  CString *s = (CString*)lparam;<br />
  TRACE0(*s);  // this shows my string<br />
<br />
  int pos = s->Find(_T("#@@#")); // shows the position where it is found, OK<br />
  TRACE0(s->Left(pos)); // gives me crap<br />
  TRACE0(s->Right(s->GetLength()-(pos+4))); // crap to, or Access Violations, etc<br />
  <br />
  delete s;<br />
<br />
<br />

So basically when I show the string, compute a position or show the length of *s everything is fine.
When I just want a part of the string, the first or last, I get a lot of crap or the program just crashes.

When I do all of that splitting in a normal procedure whit normal CString (not dynamically allocated), I get the results thaat I want, namely he part before #@@# and the part after that.

Any ideas how I can let this Left/Right splitting thing work on dynamic CStrings?

tia

Wim

Re: Problem splitting dynamically allocated CString

Gary R. Wheeler26-Jan-03 5:18

Gary R. Wheeler

26-Jan-03 5:18

Try setting a watchpoint (breakpoint on a data address) on s after you create it, and before the PostMessage call. It sounds like something else is modifying it. Also, have you single stepped through the OnSendString function, and watched the contents of s in the Watch window?

Software Zen: delete this;

Re: Problem splitting dynamically allocated CString

Ted Ferenc26-Jan-03 9:33

Ted Ferenc

26-Jan-03 9:33

I don't think what you are doing is allowed, in effect posting a class, I am sure someone will confirm/deny that, so why not do:-

CString *s = new CString();<br />
s->Format("%s#@@#%s", _T("Error"), _T("ErrorMessage"));<br />
TCHAR *sz = new char[s.GetLength() + 1);<br />
strcpy(sz, s->GetBuffer(0));<br />
PostMessage(UWM_SENDSTRING, (WPARAM)i, (LPARAM)sz);

Note the code is not 100% correct, e.g. strcpy should not be used if you are using UNICODE

If I have seen further it is by standing on the shoulders of Giants. - Isaac Newton 1676

Re: Problem splitting dynamically allocated CString

Garth J Lancaster26-Jan-03 14:33

Garth J Lancaster

26-Jan-03 14:33

This is probablya bit late (its a public holiday down here in Australia, but I got suckered into coming into the office anyway)

anyway, see this link for an explanation and working code on posting CStrings (look for "Passing Pointers in Messages") - Note well one of Joe's comments "However, if you ever plan to use PostMessage to pass a pointer to an object, then you are constrained to always use a static or heap-based object"

http://www.pgh.net/~newcomer/messages.htm[^]

Hope this helps ...

'G' <- Grinch !!!

Re: Problem splitting dynamically allocated CString

Wim Jans26-Jan-03 22:51

Wim Jans

26-Jan-03 22:51

Hi Garth,

Thanks for the advice.
Strangely enough, the piece of code I posted comes from another essay of Mr. Newcomer I read about threads[^].
There was a reference to the article you mentioned. So probably I missed something reading the articles, or I'm just a bad cut&paste person.
I will read these articles again tonight and see if I missed something, else I just send 2 messages (errorcode and errormessage) as it seems to work (Using watch variables) if I don't tamper around with the strings.

Thanks and enjoy your holiday

Wim

Re: Problem splitting dynamically allocated CString

Garth J Lancaster27-Jan-03 10:12

Garth J Lancaster

27-Jan-03 10:12

Wim Jans wrote:
) if I don't tamper around with the strings

Hi Wim - I think it comes down to that particular phrase ... when I worked in San Diego recently I worked on a project that had to modify a CString .. yuck !!! there's a particular set of hoops you have to go through - something like CString.ReleaseBuffer().. I think this is also discussed by Joe Newcomer, under his MVP tips 'CString Management' ... its still a pain in the rear though

good luck !

Creation of child dialogs

annona25-Jan-03 23:31

annona

25-Jan-03 23:31

i am using SDI MFC application. i am trying to generate many modeless dialogs in child style at the same time to display drawen charts.i use it in child styleso i can apply cascadewindows(....) function. but that leads that the dialogs is misdrawed.it's fine in pop style but i can't make it cascaded or tiled. how can i do so?????????? OMG | :OMG:

question about CRITICAL_SECTION.

George225-Jan-03 22:17

George2

25-Jan-03 22:17

Hi, everyone!

I have two samples on CRITICAL_SECTION, I want to know
the difference between them.

Sample 1:

--------
CRITICAL_SECTION cs;

EnterCriticalSection(&cs);
//code block1
LeaveCriticalSection(&cs);

EnterCriticalSection(&cs);
//code block2
LeaveCriticalSection(&cs);
--------

Sample 2:

--------
CRITICAL_SECTION cs1;
CRITICAL_SECTION cs2;

EnterCriticalSection(&cs1);
//code block1
LeaveCriticalSection(&cs1);

EnterCriticalSection(&cs2);
//code block2
LeaveCriticalSection(&cs2);
--------

I think in sample 1, code block 1 and code
block 2 can not be executed simultaneously.

But I sample 2, code block 1 and code
block 2 may be executed simultaneously.

Am I correct?

Thanks in advance,
George

Re: question about CRITICAL_SECTION.

Renjith Ramachandran26-Jan-03 0:19

Renjith Ramachandran

26-Jan-03 0:19

George2 wrote:
CRITICAL_SECTION cs1;
CRITICAL_SECTION cs2;

EnterCriticalSection(&cs1);
//code block1
LeaveCriticalSection(&cs1);

EnterCriticalSection(&cs2);
//code block2
LeaveCriticalSection(&cs2);

hi george

EnterCriticalSection() is a blocking function, that will only returns when the calling thread get the ownership.your examle code doesnot excecuet simultaniosly

If u wanna that
use TryEnterCriticalSection() API, that will returns immediatly

~CodeTheDreams~

Re: question about CRITICAL_SECTION.

George226-Jan-03 1:29

George2

26-Jan-03 1:29

Thanks, Renjith pal!

In such case,

1. Thread 1 enters code block 2, before it leaves code block 2,
for some reason, it sleeps;

2. Thread 2 enters code block 1;

3. for some reason, thread 1 wakes up and run code block 2,

So in my case, code block 1 and code block 2 could run simultaneously.

Am I correct? But in my sample 1, such case would not happen.

I am not sure about my two samples, so I want to listen to others.

Thanks in advance,
George

Re: question about CRITICAL_SECTION.

Mike Nordell26-Jan-03 1:56

Mike Nordell

26-Jan-03 1:56

George2 wrote:
But I sample 2, code block 1 and code
block 2 may be executed simultaneously.

In different threads, yes.

It's like a mutex with a twist - you can reenter an already entered critical section from within the same thread.

Re: question about CRITICAL_SECTION.

George226-Jan-03 2:10

George2

26-Jan-03 2:10

Thanks, Mike pal!

Do you mean my original opinion about two cases
are correct?

Cheers,
George

Re: question about CRITICAL_SECTION.

peterchen26-Jan-03 6:33

peterchen

26-Jan-03 6:33

yes (i.e. yes it's correct, and yes I guess that is what Mike means)

The main difference between a mutex and a critical section is that a CS is bound to a process, while a mutex can be used cross-process.

It's a royal pain to watch a sex drugs and rock'n'roll design decay into an aids crack and techno implementation [sighist] [Agile Programming] [doxygen]

Re: question about CRITICAL_SECTION.

George226-Jan-03 14:18

George2

26-Jan-03 14:18

Thanks, peterchen pal!

George

Error: Inaccurate System Timer

Edwin Geng25-Jan-03 21:54

Edwin Geng

25-Jan-03 21:54

My program gets the following error sometimes under Window Me.

-----------------------------------------
Inaccurate System Timer
Restart after reset of system timer
Press Enter to End.
-----------------------------------------

Is there an explanation why this happens?

Thanks in advance.

Edwin Geng

Re: Error: Inaccurate System Timer

Gary R. Wheeler26-Jan-03 5:23

Gary R. Wheeler

26-Jan-03 5:23

Edwin, you need to post more information. Is this a message from your application? Is it a message from the operating system? What happens if you press Enter? What are the circumstances when you get the error, and when you don't get the error?

Software Zen: delete this;

fatal error LNK1104: cannot open file "nafxcw.lib"

jimNLX25-Jan-03 21:07

jimNLX

25-Jan-03 21:07

Why do I get this error how do I correct it?

I looked in the help files and tried their suggestiong, but they didn't work.

Thanks...!

Re: fatal error LNK1104: cannot open file "nafxcw.lib"

bryce25-Jan-03 23:37

bryce

25-Jan-03 23:37

La doc nous dit que :

Static Library Versions Library Description

NAFXCW.LIB Release version
NAFXCWD.LIB Debug version (default)
UAFXCW.LIB Release version with Unicode support
UAFXCWD.LIB Debug version with Unicode support

Il faut la version PRO de Visual Studio pour compiler en Static

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.