Q116240: FIX: Compiler Errors Initializing const Reference to an Array

Article: Q116240
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC kbVC100bug kbVC150bug kbVC200bug kbVC400bug kbVC410bug kbVC42
Last Modified: 11-FEB-2002

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The information in this article applies to:

- The C/C++ Compiler (CL.EXE), used with:
   - Microsoft C/C++ for MS-DOS 
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5 
   - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 4.1, 4.2, 5.0, 6.0 
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SYMPTOMS
========

Initializing a "const" reference to an array with a "non-const" array causes
incorrect compiler errors to be generated. Two such errors are C2607 and C2561.

CAUSE
=====

The C++ compiler does not properly handle initialization of a "const T&",
where T is an array. For example, you should be able to initialize a variable of
type "const float (&ref)[3][2]" with a variable of type "float [3][2]", but
the compiler does not handle this case. Furthermore, interactions between const
declarations and typedefs of arrays do not work in all circumstances.

RESOLUTION
==========

To work around the problem, either do not use the const specifier or add
explicit casts to the appropriate const types.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

This problem was corrected in Microsoft Visual C++ .NET.

MORE INFORMATION
================

The sample code below demonstrates the problem. Compiling it yields at least one
of the following error messages:

  error C2607: 'initializing' : cannot implicitly convert a 'int [3][2]' to a
  'int __near &[3][2]' that is not const

  error C2561: 'getMtx' : function must return a value

To work around the problem, use each commented line in the program to replace the
line immediately above it.

Note: Simply removing the const specifier from the getMtx function's return type
eliminates the problem.

Sample Code
-----------

  /* Compile options needed: none
  */ 
  typedef int Matrix[3][2];

  class Data
  {
      Matrix Mtx;
      const Matrix& getMtx();
      // const int (&getMtx() const)[3][2];
  };

  inline const Matrix& Data::getMtx()
  // inline const int (&Data::getMtx() const)[3][2]
  {
      return Data::Mtx;
      // return (const int (&)[3][2])Data::Mtx[0][0];
  }

Additional query words: kbVC400bug 8.00 8.00c 9.00

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Keywords          : kbCompiler kbCPPonly kbVC kbVC100bug kbVC150bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug kbNoUpdate 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : :1.0,1.5,2.0,4.0,4.1,4.2,5.0,6.0
Issue type        : kbbug
Solution Type     : kbfix

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