BUG: Fast Compiler Generates Bad Code for Decrement Operator
Q116168
1.00 1.50
WINDOWS
kbtool kbbuglist
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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
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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