FIX: Private Copy Constructor Called Without Proper Access

• 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

SYMPTOMS

After declaring the only copy constructor in a class with an access of "private", the constructor is called when access should not be allowed. For example, when an instance of the class is passed as a parameter to a function, the copy constructor is used to initialize the parameter; this should be allowed only if the function has "private" access.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ version 5.0.

MORE INFORMATION

The following sample code demonstrates this problem.

Sample Code

   /* Compile options needed: none
   */

      #include <iostream.h>

      class aClass
      {
      private:
          int i;
          aClass(const aClass& x) { cout << "private copy constructor" <<
      endl; };

      public:
          aClass(int j) : i(j) {};
      };

      int func(aClass x) { return 0; };

      int main(void)
      {
          int n;
          aClass a(1);

          n = func(a);  //Copy constructor gets called anyway.

          return 0;
      }