Q140670: FIX: Using Run-Time Type Info May Cause Memory Leak Report

Article: Q140670
Product(s): Microsoft C Compiler
Version(s): 4.00 4.10
Operating System(s): 
Keyword(s): kbCRT kbVC
Last Modified: 03-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 4.0, 4.1 
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SYMPTOMS
========

When exiting a debug application that uses run-time type information (RTTI) and
calls the 'name' member function of the type_info class, Visual C++ reports
"Detected memory leaks!" in the output window.

CAUSE
=====

When you call the 'name' member function of the type_info class, it incorrectly
allocates a _NORMAL_BLOCK buffer to hold the type name. This can cause a memory
leak to be reported incorrectly when you run a debug version of the program.

RESOLUTION
==========

The reported memory leak can be ignored.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem was corrected in Visual C++, 32-bit
Edition, version 4.2.

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

When you call the 'name' member function of the type_info and then later call
_CrtDumpMemoryLeaks, memory leaks are incorrectly reported. The following sample
code demonstrates the problem.

Sample Code
-----------

  /* Compile options needed: /D_DEBUG
  */ 

  #include <typeinfo.h>
  #include <iostream.h>
  #include <crtdbg.h>

  struct test {};

  void main()
  {
      test t;
      typeid(t).name();
      _CrtDumpMemoryLeaks();
  }

You would see messages similar to the following in the debug tab of the output
window:

  

  Loaded symbols for 'E:\WINNT35\system32\MSVCR40D.DLL'
  Detected memory leaks!
  Dumping objects ->
  {44} normal block at 0x002D2390, 12 bytes long.
  Data: <struct test > 73 74 72 75 63 74 20 74 65 73 74 00
  Object dump complete.
  The program 'E:\temp\Text1.exe' has exited with code 1 (0x1).

NOTE: If you are using the 'name' member function within an MFC application, the
leaks will be reported even if you do not explicitly call _CrtDumpMemoryLeaks.
MFC calls this function automatically when the application terminates.

Additional query words: kbVC400bug 4.00 4.10 vcfixlist420

======================================================================
Keywords          : kbCRT kbVC 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbVC410
Version           : 4.00 4.10
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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