Q143207: PRB: Common Problems When Using STL with STD Namespace

Article: Q143207
Product(s): Microsoft C Compiler
Version(s): 4.00
Operating System(s): 
Keyword(s): kberrmsg
Last Modified: 03-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, version 4.0 
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SYMPTOMS
========

Case One
--------

When compiling a file that uses the Standard Template Library (STL), you may see
the following warning and error when using the std namespace, which is required
when using the STL with MFC:

  {stl directory}\iterator.h(65) : warning C4114: same type qualifier
  used more than once

  {stl directory}\defalloc.h(124) : error C2661: 'new' : no overloaded
  function takes 2 parameters

Case Two
--------

In addition, you may get this different set of errors:

  {include directory}\new.h(80) : error C2061: syntax error : identifier
  'THIS_FILE'

  {include directory}\new.h(80) : error C2091: function returns function

  {include directory}\new.h(80) : error C2809: 'operator new' has no formal
  parameters#endif

  {include directory}\new.h(80) : error C2065: 'ptr' : undeclared identifier

Case Three
----------

Once the previous two cases are resolved, you may get link errors. The errors you
may receive take this form:

  error LNK2001: unresolved external symbol "SymbolName"

Here SymbolName is a C Run-Time (CRT) symbol prefaced by the std:: namespace
name.

RESOLUTION
==========

Warning C4114 is superfluous and can be ignored. You can disable the warning by
using a '#pragma warning' directive. Error C2661 requires that you include New.h
in your source file.

The second set of errors occurs if you add the STL include directive after the
following definitions and do not include New.h among your include directives:

     #ifdef _DEBUG
     #define new DEBUG_NEW
     #undef THIS_FILE
     static char THIS_FILE[] = __FILE__;
     #endif

Including New.h will work around this problem as well. Note that these
definitions are no longer necessary in MFC code and can be deleted.

The third set of errors from the linker can be resolved by including the
appropriate header files from the CRT above the declaration for the std
namspace. You can determine which header file must be included by looking at the
symbol listed in the linker error. Remove the leading std:: from the symbol, and
then search for the symbol in the CRT header files. This file was included by
the STL headers. You need to include this header explicitly before the namespace
declaration. In the Case Three Sample Code section in this article, you can see
Iostream.h is the header that must be included at global scope.

STATUS
======

This behavior is by design.

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

Sample Code to Reproduces Behavior Described in Case One
--------------------------------------------------------

     /* Compile options needed: none
     */ 

     //#include <new.h>   // Required to avoid C2661 error.

     namespace std {
     #include <vector.h>
     }

     std::vector<char> test;

Sample Code to Reproduces Behavior Described in Case Two
--------------------------------------------------------

     /* Compile options needed: /c /D_DEBUG /DNOMINMAX
     */ 

     #include <afxwin.h>  // or stdafx.h in a default AppWizard project.
     //#include <new.h>   // Required to avoid this problem.

     #ifdef _DEBUG
     #define new DEBUG_NEW
     #undef THIS_FILE
     static char THIS_FILE[] = __FILE__;
     #endif

     namespace std {
     #include <vector.h>
     }

Sample Code to Reproduces Behavior Described in Case three
----------------------------------------------------------

     /* Compile options needed: none
     */ 

     //#include <iostream.h>     // Required to avoid LNK2001 error
     #include <new.h>

     namespace std {
     #include <vector.h>
     }

     std::vector<int> test(0,10);

Additional query words: MFC

======================================================================
Keywords          : kberrmsg 
Technology        : kbVCsearch kbVC400 kbAudDeveloper
Version           : 4.00
Issue type        : kbprb

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

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