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

• 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, 1.51, 1.52 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 4.1,

       4.2, 5.0
  

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

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';
   }