FIX: C4114 Warning When Using Templates and Const Keyword

• The compiler included with: - Microsoft Visual C++, 32-bit Edition, versions 2.x, 4.0, 4.1, 4.2

SYMPTOMS

Using a class or function template may incorrectly generate a C4114 warning. The sample code in this article demonstrates a case where this occurs.

CAUSE

The compiler incorrectly expands the type of the function parameter to const T as it expands a template with type const T when the definition of a function or member function template has a parameter that takes a const T.

The Help file gives the following information for C4114:

• Same type qualifier used more than once.
• A type qualifier (const, volatile, signed, or unsigned) was used more than once in the same type declaration or definition. The second occurrence of the qualifier was ignored. This is a warning when Microsoft extensions are enabled (/Ze) and an error when extensions are disabled (/Za).
• The following is an example of this warning:

     volatile volatile int i;   // warning
  
  

RESOLUTION

This warning can be safely ignored. To disable all occurrences of this warning, use the #pragma warning preprocessor directive. The Help file demonstrates how to use this pragma.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ version 5.0.

MORE INFORMATION

Sample Code to Reproduce Problem

   // test.cpp
   // Compile options needed - none
   template <class T>
   struct f
   {
     void goo( const T & r){ T t=r;};
   };

   void main()
   {
       f<const int> h;

       // the following line of code causes
       // goo( const const int ) to be expanded
       h.goo( 2 );
   }