FIX: _CRTDBG_MAP_ALLOC Environment Var References Incorrect

• The C Run-Time (CRT), used with:
  • Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 5.0, 6.0

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:

Keywords : kbCRT kbDocs kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix
Version : winnt:4.0,4.1,4.2,5.0,6.0
Platform : winnt
Issue type : kbbug