BUG: Compiler Errors Initializing const Reference to an Array

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 4.0, 4.1, 4.2,

       5.0
  

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.

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

RESOLUTION

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

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"

   -or-

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

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];
   }