PRB: Common Problems When Using STL with STD Namespace (143207)

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.

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);