Knowledge Base

FIX: IDE Debugger Truncates Floating Point Numbers

Article ID: 155622

Article Last Modified on 12/10/2003

The Integrated Debugger, when used with:
- Microsoft Visual C++ 5.0 Learning Edition
- Microsoft Visual C++ 5.0 Learning Edition
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 4.0 Professional Edition
- Microsoft Visual C++ 4.1 Subscription
- Microsoft Visual C++ 4.2 Professional Edition

This article was previously published under Q155622

SYMPTOMS

If you change the Language Settings under the operating system to a language that uses a comma as the decimal separator, recalculating any floating point numbers in the QuickWatch window in the integrated debugger truncates the floating point number. Thereafter, incorrect results may be generated from program execution. To reproduce the problem, please see the "More Information" section below.

The following language settings may cause this problem.

   German      Italian    Portuguese    Swedish   Norwegian
   Indonesian  Icelandic  French        Finnish   Dutch
   Danish      Catalan    Basque

RESOLUTION

To work around the problem, use one of the following suggestions:

In the QuickWatch window, cast the variable you plan to watch to the proper type. For example, if you plan to watch variable "a" in the following program, because "a" is defined as type double, cast it to a double in the QuickWatch window. That is, type "(double)a" (without the quotation marks) in the QuickWatch window.

-or-
In the QuickWatch window, add zero to the variable. For example, in the following program, type "a+0" (without the quotation marks) in the QuickWatch window to watch variable "a".

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

You can use the following steps to reproduce the problem:

Use Control Panel to change language settings to German(Standard), then reboot the system.

Build an application using the source file below:

   /* Compile options needed: Developer Studio default console application
   */ 

   #include <stdio.h>

   void main()
   {
      double a = 1.99;
      double b;

      printf("a = %g\n", a);

      b = a;  // At this point do QuickWatch and Recalculate for 'a'.

      printf("b = %g\n", b);
   }

Start debugging and get to the commented line "b = a".
Use QuickWatch for "a"; it will show the correct value 1.99.
Click Recalculate one or two times more.

Result: The value of "a" is changed to 1.0, and the program's output will be wrong when execution is continued to next line.

Keywords: kbbug kbfix kbide kbprogramming kbvc500fix kbdebug KB155622