Q87638: PRB: C4512 "Class": Assignment Operator Could Not Be Generated

Article: Q87638
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,1.52,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC410 kb
Last Modified: 01-APR-2002

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The information in this article applies to:

- Microsoft C/C++ for MS-DOS 
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52 
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0, 6.0 
- Microsoft Visual C++.NET (2002) 
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SYMPTOMS
========

The following warning may be generated when Microsoft C/C++ version 7.0 or later
is used to compile a C++ source file that uses a class containing a const data
member:

  C4512: <class_name> : assignment operator could not be generated

where class_name is the name of the class containing the const data member.

CAUSE
=====

The compiler will generate an assignment operator function for a class that does
not define one. This assignment operator is simply a memberwise copy of the data
members of an object. Because const data items cannot be modified after
initialization, if the class contains a const item, the default assignment
operator would not work.

RESOLUTION
==========

The C4512 warning will not prevent the generation of an object module. The
warning can be eliminated by any of the following methods:

- Explicitly define an assignment operator for the class.

  -or-

- Remove the const data item from the class.

  -or-

- Use the #pragma warning statement.

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

The following sample C++ code demonstrates this situation.

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

  /* Compile options needed: /W4
  */ 

  #include <iostream.h>

  class base
  {
     const int a;

  public:
     base(int val = 0) : a(val) {}
     int get_a(void) { return a; }
  };

  void main()
  {
     base first;
     base second(5);

     cout <<
     "First = " <<
     first.get_a() <<
     '\n';

     cout <<
     "Second = " <<
     second.get_a() <<
     '\n';
  }

Additional query words: 8.00 8.00c 9.00 9.10

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Keywords          : kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC410 kbVC420 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbZNotKeyword3 kbVC410 kbVC420 kbVC500 kbVC600 kbVC151 kbVC200 kbVC210 kbVC32bitSearch kbVC16bitSearch kbVC152 kbVCNET kbVC500Search
Version           : :1.0,1.5,1.51,1.52,2.0,2.1,4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

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