Re: malloc with Studio Express 2008 C++

From:
"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 7 Jan 2009 13:22:35 -0600
Message-ID:
<uOF9M1PcJHA.1860@TK2MSFTNGP04.phx.gbl>
Nathan Mates wrote:

In article <ecF20mIcJHA.5748@TK2MSFTNGP03.phx.gbl>,
James Williams <Jim_L_Williams@hotmail.com> wrote:

I am trying to convert an old dos program and when trying to run the
app, malloc keeps throwing an error saying allocation: bad memory
block type.


  Given that, my gut feeling is this: something's already trashed
memory, and malloc is just the function that notices the problem


Yes, it looks like a buffer overrun bug. Could be caused by making
assumptions about the size of a pointer, which would appear during a 16-bit
to 32-bit port, or could be a bug in the original 16-bit code that just
happened not to cause a crash.

first. I really recommend that you make a Debug build (with debug
C Runtime libs, which is the default configuration), and sprinkle
in a bunch of calls to _CrtCheckMemory() -- see
http://msdn.microsoft.com/en-us/library/e73x0s4b(VS.71).aspx
As that page says, it's good to sprinkle in a bunch of calls to

  _ASSERTE(_CrtCheckMemory());

throughout the code. (Note: you'll need to #include <crtdbg.h> to get
both _ASSERTE() and _CrtCheckMemory() functions.) Basically, I suspect
you'll see _CrtCheckMemory() going unhappy at some point, before it
gets to your call to malloc that's failing.

Nathan Mates

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