PRB: Setting DECIMALS to 15 or More Produces Incorrect Result

ID: Q131003

3.00 WINDOWS kbprg kbprb

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 3.0
Microsoft FoxPro for Windows, version 2.6a

SYMPTOMS

When you use SET DECIMAL to set DECIMAL to 15 or more, certain mathematical calculations produce an incorrect result.

CAUSE

Some numbers when represented in a floating point format have no exact representation. For example, this is 1/3 where as .33333333 is in fact slightly less than 1/3.

However, some numbers that do have exact floating point representations still exhibit this behavior. See the "Steps to Reproduce Behavior" section for an example.

STATUS

Microsoft is researching this issue and will post new information here in the Microsoft Knowledge Base as it becomes available.

Steps to Reproduce Problem

1. Launch Visual FoxPro.

2. In the Command window, enter the following, one line at a time:

   SET DECIMALS TO 14
   ? 32.16/4

3. Observe the results in the active output window. You should see

   8.04000000000000. This is exactly correct.

4. Repeat step 2, but this time set decimals to 15.

5. Observe the results. You should see 8.039999999999999. This is

   incorrect, and demonstrates this problem.

Additional reference words: 3.00 VFoxWin KBCategory: kbprg kbprb KBSubcategory: FxprgSet

Keywords          : FxprgSet 
Version           : 3.00
Platform          : WINDOWS