## BUG: Fast Compiler Generates Bad Code for Decrement Operator

Q116168

    1.00 1.50
    WINDOWS
    kbtool kbbuglist

    ----------------------------------------------------------------------
    The information in this article applies to:

     - The Microsoft C/C++ Compiler (CL.EXE), included with:
       Microsoft Visual C++ for Windows, versions 1.0 and 1.5
    ----------------------------------------------------------------------

    SYMPTOMS
    ========

    The fast compiler may generate bad code for statements that use the
    decrement operator and may assign the decremented value back to the
    variable being decremented.

    RESOLUTION
    ==========

    This problem can be worked around either by compiling using the optimizing
    compiler or by restructuring the code. Use of the optimizing compiler can
    be forced by using the /f- compiler switch. The sample code in the "MORE
    INFORMATION" section below can be used both to illustrate the problem and
    to show how the code can be restructured to work around the problem.

    STATUS
    ======

    Microsoft has confirmed this to be a bug in the C/C++ compiler for
    MS-DOS, versions 8.0 and 8.0c. We are researching this problem and will
    post new information here in the Microsoft Knowledge Base as it becomes
    available.

    This is not a problem with the 32-bit C/C++ compiler, version 8.0.

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

    The following sample code can be used to demonstrate the problem.

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

    /* Compile options needed: /f
    */
       #include <iostream.h>

       enum color { red, green, blue };

       void main()
       {
           color ColorEntered;
           int choice, first = 3, last = 4;

           do
           {
               cout << "\nEnter a 0 or 1. Enter 2 to end: ";
               cin >> choice;
               ColorEntered = (color)choice;

               switch(ColorEntered)
               {
                   case red:
                       cout << "RED" << endl;
                       break;

                   case green:
                       cout << "GREEN" << endl;

                       // The fast compiler generates bad code for this
                       // statment:
                       first = ( (first > 0) ? (first--) : (last) );

                       // To work around the problem restructure the code
                       // as follows:
                       /*
                       if( first > 0 )
                           first--;
                       else
                           first = last;
                       */

                       cout << "value of first: " << first << endl;
                   break;

                   case blue:
                       cout << "BLUE" << endl;
                       cout << "Ending" << endl;
                       break;

                   default:
                       cout << "Value out of range, ending" << endl;
                       ColorEntered = blue;
                       break;
               }

           } while(ColorEntered != blue);
       }

    Additional reference words: 1.00 1.50 8.00 8.00c
    KBCategory: kbtool kbbuglist
    KBSubcategory: CodeGen

Keywords : kb16bitonly
Issue type :
Technology :

Last Reviewed: December 22, 1999 © 2001 Microsoft Corporation. All rights reserved. Terms of Use.