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Q141958: FIX: _CRTDBG_MAP_ALLOC Environment Var References Incorrect

Article: Q141958
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbCRT kbDocs kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix
Last Modified: 30-JUL-2001

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The information in this article applies to:

- The C Run-Time (CRT), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

There are several incorrect references to setting the _CRTDBG_MAP_ALLOC
environment variable in the documentation for the debug version of the C
run-time library.

It is not an environment variable, but rather a preprocessor constant. This
symbol needs to be defined either in the code with a #define or from the command
line with the compiler /D option.


STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

MORE INFORMATION
================

If you look in the header file, Crtdbg.h, you will see that this symbol is used
as a preprocessor constant.

There are two places where this symbol is referred to as an environment variable
in the Run-Time Library Reference. From the Help contents, go to "Debug Version
for the Run-Time Library" in the Run-Time Library Reference book, go to "Memory
Management and the Debug Heap" and then "Using the Debug Version Versus the Base
Version." The second sentence in the third paragraph states, "Applications that
do not want to convert their malloc calls to _malloc_dbg can obtain the source
file information by defining the _CRTDBG_MAP_ALLOC environment variable." In the
next paragraph, it also states, "When _DEBUG is not defined, calls to malloc are
not disturbed, calls to _malloc_dbg are resolved to malloc, the
_CRTDBG_MAP_ALLOC environment variable is ignored, ..."

Additional query words:

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Keywords          : kbCRT kbDocs kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:4.0,4.1,4.2,5.0,6.0
Issue type        : kbbug
Solution Type     : kbfix

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