BUG: Compiler Errors Initializing const Reference to an Array

ID: Q116240

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

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.

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


Keywords          : kbCompiler kbCPPonly kbVC kbVC100bug kbVC150bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug 
Version           : winnt:1.0,2.0,4.0,4.1,4.2,5.0,6.0
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: April 15, 1999