DOCUMENT:Q150573  03-AUG-2001  [visualc]
TITLE   :FIX: C2084 When Template Class Constructor Has No Body
PRODUCT :Microsoft C Compiler
PROD/VER:4.1 4.2
OPER/SYS:
KEYWORDS:kbCompiler kbCPPonly kbVC kbVC500fix

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The information in this article applies to:

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

NOTE: the sample code in this article gives examples of explicit versus implicit
template instantiation.

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

Additional query words: kbVC400bug

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Keywords          : kbCompiler kbCPPonly kbVC kbVC500fix 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : 4.1 4.2
Issue type        : kbbug
Solution Type     : kbfix

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