Re: CByteBuffer implementation passed between modules

From:
"Mihai N." <nmihai_year_2000@yahoo.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Thu, 13 Jul 2006 01:23:31 -0700
Message-ID:
<Xns97FFE2A4BC62MihaiN@207.46.248.16>

Well duh, RTL stands for Run Time Library, doesn't it?

Nope. Stands for Right-To-Left :-)
CRT is usualy "C Runtime Library"

Ok, after the cheep joke, something serious.

I would recomend making sure the crash is actually caused by the exe/dll
scenario.
In many cases you get a crash at delete because there is a copy happening
somewhere.
When you have allocated resources like this, you allways have to define
a copy-constructor and the assignement operator.
In there you either have to do a ref-count (with a lot of care, considering
what happens when several objects modify the same buffer), or make a copy of
the buffer (safer and easyer).

Let's say you have your class:
     CByteBuffer a, b;
     a.Set( buf, 10 );
     b = a;

Now, b will use the default assignment (copy member by member), meaning the
b.m_pBuf will point to the same buffer as a.m_pBuf
At destruction time, the second object being distroyed will try to delete a
pointer that was already deleted. Crash!

Other problems I can think of (not for this crash, but for others :-)
     Set (LPVOID p, size_t size)
     {
     m_pBuf = new BYTE[size];
     memcpy (m_pBuf, p, size);
     };

Now consider this:
     CByteBuffer a;
     a.Set( buf, 10 );
     a.Set( buf, 20 );
Memory leak!

Then you also need the size of the source buffer.
     CByteBuffer a;
     BYTE *buf = new BYTE[10];
     a.Set( buf, 10000000 );
Set will try to access way beyond the end of buffer, with a (possible)
violation. Crash!

Mihai

--
Mihai Nita [Microsoft MVP, Windows - SDK]
http://www.mihai-nita.net
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