FIX: C2440 Caused by Template Function with Const Pointer

• The C/C++ Compiler (CL.EXE), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 4.2, 4.2b, 5.0

SYMPTOMS

The compiler generates the error C2440, when compiling a template function with a const pointer of class T as an argument, where class T is a template parameter.

C2440: 'conversion' : cannot convert from 'type1' to 'type2'

RESOLUTION

Starting with Visual C++ 5.0, explicitly specify the template arguments when calling the template function.

The sample code below demonstrates the problem and the workaround.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97 Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

The following sample code demonstrates the problem.

Sample Code

   /*
   * Compiler Options: None
   */ 

   template <class T> T* func(const T*p)
   {
      return 0;
   }

   int main()
   {
      const int *i=0;
      int*j = func(i);    // erroneous C2440 here

      return 0 ;
   } 

Sample Code

   /*
   * Compiler Options: None
   */ 

   template <class T> T* func(const T*p)
   {
      return 0;
   }

   int main()
   {
      const int *i=0;
      int*j = func<int>(i);

      return 0 ;
   } 

Additional query words: CL

Keywords : kbcode kbprg kbCompiler kbCPPonly kbLangCPP kbVC kbVC420bug kbVC500bug kbVS97sp1fix
Version : 4.2 4.2b 5.0
Platform : NT WINDOWS
Issue type : kbbug