FIX: C2084 When Template Class Constructor Has No Body

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft Visual C++, 32-bit Edition, version 4.1, 4.2

SYMPTOMS

The following error occurs when a template class is explicitly instantiated and it has more than one constructor, at least one of which does not have a body defined and at least one of which is defined outside of the class:

   error C2084: function '<function name>' already has a body

WORKAROUND

• This is the preferred workaround. Give every constructor a body. The body is defined inside or outside the template class.

  -or-

• Place all the existing constructor bodies inside the template class definition.

  NOTE: You get the following warning associated with the explicit instantiation request:

        warning C4661: <symbol> : no suitable definition provided for
        explicit instantiation request
  

  This warning is issued when a template class does not have all its members defined and an explicit instantiation request is made. This warning also causes the compiler to ignore the instantiation request.

  -or-

• Instantiate the template class implicitly rather than explicitly. In this case, the instantiation occurs when declaring an object using the template class, but the C2084 does not.

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

   /* Compile options needed: /c
   */

   template <class T>
   class A {
   public:
       A();             // give this ctor a body for workaround 1
       A(const T&);
   };

   template <class T> A<T>::A(const T&) {}; // move this ctor body
                                            // inside the class
                                            // definition for
                                            // workaround 2

   template A<int>;     // this is an explicit instantiation -
                        // comment this line out and uncomment the
                        // next line for workaround 3
   // A<int> x = 3;     // this is an implicit instantiation

Keywords          : CPPIss vcbuglist400 vcfixlist500 kbprg
Version           : 4.1 4.2
Platform          : NT WINDOWS
Issue type        : kbbug
Solution Type     : kbfix