C / C++ / MFC

18-Jun-07 11:17

Call me a late bloomer, but I've been maintaining code for MFC 4.2 and 7.1 for a while and I just noticed in the Visual C++ 2003 documentation does not indicate that CObject::operator new throws MFC exceptions.

What happended to CMemoryException from MFC 4.2?

I'm not sure if this new operator (For CObject) throws or returns a NULL pointer in MFC 7.1. Sorry about the silly question.

Mark Salsbery18-Jun-07 11:33

18-Jun-07 11:33

Looking at the source code in VS 2003 .NET, CObject::operator new doesn't throw any MFC
exceptions.

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

bob1697218-Jun-07 12:01

18-Jun-07 12:01

I saw the ::operator new in there but it kinda confuses me as to what it does in the Microsoft compiler. (By default, if there is such a thing)

I've been crawling through MSDN for Visual C++ 2003 for a bit and it's really not clear if ::operator new throws or returns a NULL in Visual C++ 2003.

Mark Salsbery18-Jun-07 12:11

18-Jun-07 12:11

bob16972 wrote:
and it's really not clear if ::operator new throws or returns a NULL in Visual C++ 2003

Have you seen this article?

The new and delete Operators[^]

I didn't say it would be any more clear after reading this article Wink | ;)

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

Bram van Kampen18-Jun-07 14:45

Bram van Kampen

18-Jun-07 14:45

Have I Seen this Article before? No,

Reading the Original Question, I had not seen this article either! Sounds quite Drastic,BUT there is only one additional burden, and that is to register an exception handler as early as possible,(i.e Before any NULL Pointer can occur in User Code. InitApp() seems to be a good place.

At the other hand, very many of us spend most of our coding time to write 'if's' and 'but's to deal with faulting. This clutters up the general flow of the code we write. Exception handeling is in practice seldomly used as a mechanism, mainly because it is complex in nature, and not worth the bother.
This suttle change will hopefully be the impetus for people to learn about the syntax of exception handeling, and ultimately make code and program Syntax clearer.

LateNightsInNewry

bob1697218-Jun-07 15:00

18-Jun-07 15:00

Mark Salsbery wrote:
I didn't say it would be any more clear after reading this article

I gave both the local MSDN and the latest online one a go earlier today when the subject came up at work and I was thrown off guard when CObject no longer advertised that it could throw in the 2003 MSDN. I came across this article but it left a few questions still hanging.

Mark Salsbery wrote:
I didn't say it would be any more clear after reading this article

ain't it the truth.

Thanks for taking the time out to assist.

Mark Salsbery18-Jun-07 13:11

18-Jun-07 13:11

It looks like it's documented under "CMemoryException class" and here:
Exception Handling in MFC[^]

For MFC apps, CMemoryException is thrown, even on non-CObject objects.

For non-MFC apps, std::bad_alloc is thrown.

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

bob1697218-Jun-07 15:08

18-Jun-07 15:08

I came across that stuff as well but I didn't walk away with that fuzzy feeling with how they kinda make us piece it all together when they used to just come right out and tell us that the class throws CXXXXException.

I figured I'd give it a brute force test and you are right, good ole CMemoryException is still thrown so I don't have to scurry about rewriting all my 6.0 code after all.

try {

while (TRUE) {
CxObject* pObject=new CxObject();
}
}

catch (CMemoryException* e) {
TRACE("CMemoryException\n"); // Get's thrown
}

catch (CException* e) {
TRACE("CException\n");
}

catch (...) {
TRACE("Other Exception\n");
}

My machine isn't too happy now (reboot). Big Grin | :-D

Thanks for the assistance!

Mark Salsbery18-Jun-07 15:27

18-Jun-07 15:27

bob16972 wrote:
I didn't walk away with that fuzzy feeling

No kidding! Smile | :)

I had to test it too, AND I was just looking at it again (Thanks, LateNightsInNewry Poke tongue | ;-P

).

To start with, the test code in the first article I linked to (that demonstrates the new operator
throw) didn't work - well, not as I expected. That made me question all my assumptions in my
code.
Turns out, if you attempt to allocate a block too big for the platform, it breaks with a debug
message and returns NULL instead of an exception. Not a big deal, I guess - that should be caught
in the debug phase. But still, I was wondering if I had to check for NULL returns too.

Looking at the MFC source, MFC installs its own new handler and has a single static
CMemoryException object that it throws the address of.

I like your test code! Mine was more conservative (why I didn't use an infinite loop, I don't
know LOL)... borrowing from the article:

int * i_arr;
try {
   for (int i = 0; i < 1000000; i++)
      i_arr = new int[0x0fffffff];
} 
catch(...) {
   OutputDebugString("caught exception\n");
}

Cheers!
Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

Bram van Kampen19-Jun-07 14:27

Bram van Kampen

19-Jun-07 14:27

My whole horror with the Class CException is, that at the Understandable levels, it throws an exception, with a DWORD (QWORD?)number. That's quite simple, a Switch statement will sort what's going on. I can understand that concept. I also understand, that Different people writing different programs, will arrive at the Same exception numbers for different exceptions. I understand that this will be a problem when DLL's Meet.

Somehow, Microsoft devised a scheme which involved development time for derriving a new class from CException, for anything that may go wrong. I understand also that the reason for this is to be able to generate a distinct exception for each case, independent of exception numbering. At the same time, The link between Exception DWORD Numbers for exceptions, and Existing or New derrived exception classes is not very clear in the documentation.

A Point in case is, you use catch(...)in your sample code!as you know, this catches ALL Exceptions. In a Real life situation, how do you only catch those you are interested in and pass the rest on to some other handler.

LateNightsInNewry

Mark Salsbery19-Jun-07 14:58

Query interface parameter

19-Jun-07 14:58

It's actually Microsoft sample code. It worked well for my test because I could put a breakpoint
in the catch block and I could immediately see the exception class without knowing what I'd get.
In real-life, IMO, a catch(...) is pretty useless. How can you possibly know how to proceed
or if it's even safe to proceed after catching an unknown exception?

The CException class is an abstract base class that provides one interface to get an error
message. If there's a DWORD involved, it's in a derived class, and is generally added so one
has a better context to detect why the exception occurred. I'm not sure what the DWORD is you're
referring to Smile | :)

The variables added by the MFC exception classes are well documented.
With new CException-derived classes, you're on your own to add what you want.

In real life, AFAIK, exceptions shouldn't be used for simple error handling. Returning an error
code is faster and simpler.

Constructors can't return error codes so throwing an exception is the only way to indicate
failure.

Using MFC, sometimes it's not a choice. The database classes are a good example. Those
exceptions must be handled, and generally it's safe to continue after handling them, and they
also provide detailed error information for logging and/or deciding how to proceed after they
occur.

Hmm, I'm rambling pointlessly Laugh | :laugh:

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

_tasleem18-Jun-07 10:47

_tasleem

18-Jun-07 10:47

hi all i m using this line in my outlook addin project but it give error
"unresolved external symbol _IID_IMAPISession", so i search on net for that value,i foud one but when assign that value its as string when i assign that value to a CString object then it gives error cannot covert Cstring to struct _GUUId,
it tried this
#define IID_IMAPISession= "00020300-0000-0000-C000-000000000046"
this but stil same error
struct _GUID IID_IMAPISession= 00020300-0000-0000-C000-000000000046;
tell me what to do.
CComPtr<iunknown> punk;
spMailItem->get_MAPIOBJECT(&punk);
punk->QueryInterface(IID_IMAPISession, (void**)&m_pSession);
tell me what to so that it works i m stuck to that.

Regards.
Tasleem Arif

Mark Salsbery18-Jun-07 11:08

18-Jun-07 11:08

You need to include MAPIguid.h I believe.

Then you can use IID_IMAPISession.

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

_tasleem19-Jun-07 2:47

_tasleem

19-Jun-07 2:47

still same problem.

Regards.
Tasleem Arif

Mark Salsbery19-Jun-07 4:33

19-Jun-07 4:33

An unresolved external means you're missing a library.

I don't know what library you need to link to but I'll take a guess that you need to add
MAPI32.lib to your project.

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

_tasleem19-Jun-07 9:04

_tasleem

19-Jun-07 9:04

thanks, i managed to solve that erro, i was including MAPI32.lib,but i was using extended MAPI function such MapiLoginEx,Problem was that i was confused with MAPI and Extended MAPI Dll's. i searched a lot on internet some people were saying MAPI32.dll is extended MAPI some MAPIX.dll is extended MAPI, and some MAPI32x.dll is extended MAPI, i posted question on CP but found no reply.

i replaced that line with IID_IUnknown and it worked fine. Thanks for ur kind answers.

Regards.
Tasleem Arif

GDI+ documentation

Force Code18-Jun-07 7:43

Force Code

18-Jun-07 7:43

Sorry for the newbie question.
I downloaded the platform sdk from Microsoft to get the GDI+ header files and now I need some documentation. Is there any in the 2 gigabytes of krap they dump onto your system? MSDN.com is awfully slow, and I don't want to go to the World Wide Web every time I want a parameter description. There is a 'precompiled help file' in the platform sdk, 'gdicpp.hxs', and it contains GDI+ terms. However, I don't know how to open it . Drag it onto VC++ express, and it doesn't know how to open it either.

Mark Salsbery18-Jun-07 7:47

18-Jun-07 7:47

In the SDK docs...

Contents (tab)/Graphics and Multimedia/GDI+

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

Force Code18-Jun-07 8:16

Force Code

18-Jun-07 8:16

I don't know where that is - what application do I need to open? I've downloaded VC++ express and the PlatformSDK for windows server R2 2003. Im running Windows 2000.

What application opens the SDK docs?

In VC++ express, if you search for GDI+, it goes to the internet and comes back and says it didn't find anything.

I normally use Dev-C++. To me VC++ is such a joke. You open it, and immediately it starts searching the internet for "News" or what-not, even though you didn't ask for it.

Mark Salsbery18-Jun-07 8:34

18-Jun-07 8:34

Force Code wrote:
What application opens the SDK docs?

When I installed the PSDK, a program folder was created called "Microsoft Platform SDK for
Windows Server 2003 R2". In that folder is a "Platform SDK Documentation" shortcut.

Force Code wrote:
In VC++ express, if you search for GDI+, it goes to the internet and comes back and says it didn't find anything.

That's because the express edition is free. You get what you pay for Smile | :)

Force Code wrote:
To me VC++ is such a joke. You open it, and immediately it starts searching the internet for "News" or what-not, even though you didn't ask for it.

You can turn that off - go to Tools menu, Options.../Environment/Startup and select the
appropriate item in the "At startup" combobox.

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

Force Code18-Jun-07 10:08

Force Code

18-Jun-07 10:08

Mark Salsbery wrote:
When I installed the PSDK, a program folder was created called "Microsoft Platform SDK for Windows Server 2003 R2". In that folder is a "Platform SDK Documentation" shortcut.

I have "Microsoft Platform SDK for Windows Server 2003 R2", but not "Platform SDK Documentation" shortcut. Did you have to do anything to "install" the Platform SDK after downloading it? There's a setup directory, but no setup.exe. AS I said, it downloaded gigabytes so I don't know what I'm missing.

Mark Salsbery18-Jun-07 11:04