KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q139953: BUG: DATETIME Datatype Rounds Fractions of a Second

Article: Q139953
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0,5.0,5.0a,6.0
Operating System(s): 
Keyword(s): kbprogramming kbvfp kbvfp500aBUG kbvfp500bugkbbuglist
Last Modified: 10-FEB-2000

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

- Microsoft Visual FoxPro for Windows, versions 3.0, 5.0, 5.0a, 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Repeatedly adding (or subtracting) a fraction of a second to (or from) a
variable that contains a DATATIME data type results in an unexpected value being
stored in the variable.

CAUSE
=====

Visual FoxPro rounds the fraction of a second being added (or subtracted) up (or
down) to the nearest whole second and stores the rounded value in the variable.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products listed at
the beginning of this article. We are researching this problem and will post new
information here in the Microsoft Knowledge Base as it becomes available.

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

Steps to Reproduce Problem
--------------------------

1. Type the following line of code in the Command window:

     X = {1/1/95 12:00:00PM}

2. Type the following line of code in the Command window:

     Y = X + .1

3. Type the following line of code in the Command window:

     ? Y == X

The return value is True (.T.) even though you added a tenth of a second to x.

Another Demonstration of the Problem
------------------------------------

1. Type the following line of code in the Command window:

     MODIFY COMMAND test

2. In the program window produced by the previous command, type the following
  lines of code:

     *---------------------
     *-- BEGIN PROGRAM TEST
     *---------------------
     CLEAR

     LOCAL X, Y
     X = {1/1/95 12:00:00pm}
     FOR I = 1 to 5

       *-- Show which iteration you are on
       DO CASE
            CASE I = 1
                 WAIT WINDOW "Iteration 1" TIMEOUT .75
            CASE I = 2
                 WAIT WINDOW "Iteration 2" TIMEOUT.75
            CASE I = 3
                 WAIT WINDOW "Iteration 3" TIMEOUT.75
            CASE I = 4
                 WAIT WINDOW "Iteration 4" TIMEOUT.75
            OTHERWISE
                 WAIT WINDOW "Last Iteration" TIMEOUT.75
       ENDCASE

       *-- Add 1 tenth of a second to Y
       Y = X + .1

       *-- Display X
       WAIT WINDOW "X = " + TTOC(X) TIMEOUT 1

       *-- Compare Y and X
       *-- One would think the following comparison would return .F.
       WAIT WINDOW "Y == X is " + IIF(Y==X,".T.",".F.") + ;
            "  <<= First Test" + CHR(13) + ;
            "Y has been incremented" + CHR(13) + CHR(13) +;
            "Press any key to continue"

       *-- Add 1 tenth of a second to X
       X = X + .1

       *-- Compare Y and X
       *-- One would think the following comparison would return .T.
       WAIT WINDOW "Y == X is " + IIF(Y==X,".T.",".F.") + ;
            "  <<= Second Test" + CHR(13) + ;
            "X has been incremented" + CHR(13) + CHR(13) + ;
            "Press any key to continue"

       *-- Display Y
       WAIT WINDOW "Y = " + TTOC(Y) + ;
            CHR(13) + ;
            "Y has been incremented by .1 seconds" ;
            TIMEOUT 2
     ENDFOR
     *---------------------
     *-- END PROGRAM TEST
     *---------------------

3. Run the program. A one-second increase in time is displayed after five tenths
  of a second have accumulated. The incremented tenths are held by the variable
  but are never displayed until rounding the accumulated number of tenths
  results in a full second. Additionally, the comparison appears to be based on
  the rounding of the fractions of a second, not on the actual number stored to
  the variable.

Additional query words: kbvfp300 kbvfp500 kbvfp600

======================================================================
Keywords          : kbprogramming kbvfp kbvfp500aBUG kbvfp500bug kbbuglist
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP500 kbVFP600 kbVFP500a
Version           : WINDOWS:3.0,5.0,5.0a,6.0
Issue type        : kbbug

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.