Q168010: FIX: /Od May Generate Destructor for Unconstructed Temp Object

Article: Q168010
Product(s): Microsoft C Compiler
Version(s): 5.0
Operating System(s): 
Keyword(s): kbVS97sp1fix kbVS97sp2fix
Last Modified: 17-JUL-2001

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The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

The destructor for a class may be called for an unconstructed temporary when
used with the conditional operator.

RESOLUTION
==========

Use an if-else construct in lieu of the conditional operator. In most cases, the
logical not operator can be applied to the first operand while reversing the
second and third operands.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been corrected in Visual Studio 97
Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see
the following article in the Microsoft Knowledge Base:

  Q170365 Visual Studio 97 Service Packs - What, Where, and Why

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

Assuming a class C and a type T, the following conditions must be true of the
ternary expression for this bug to occur:

- The second operand is of type C.

- The third operand is of type T.

- Class C has an operator T() and a constructor, C(T).

The following sample demonstrates the problem.

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

     typedef int T;
     class C
     {
         T _i;
     public:
         C(const C& c);
         C(T);
         ~C();
         operator T();
     };
     void f(T i)
     {
         C c1(5);
         C c2 = i==0 ? c1 : i;
              //i ? i : c1; // possible workaround
     }

NOTE: MFC's CString class exhibits this behavior.

Additional query words:

======================================================================
Keywords          : kbVS97sp1fix kbVS97sp2fix 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : 5.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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