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Q133740: Null Value (.NULL.) Is a Marker - Not a Data Type

Article: Q133740
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): 
Last Modified: 15-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
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SUMMARY
=======

The null value (.NULL.) is not an actual value, it is a marker that denotes that
a memory variable or a field value is missing or unknown. If .NULL. is assigned
to a field or a variable, the field or variable's data type is not changed, but
the value is changed to NULL.

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

Steps to Demonstration Behavior
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The .NULL. value can be assigned to variables that are numeric or character as
demonstrated by these steps:

1. From the Command window, issue these commands:

     nMyvariable=200        && and press ENTER
     ? TYPE("nMyvariable")  && and press ENTER
     ? nMyvariable

  The N is displayed for nMyvariable denoting a variable of numeric type.

2. To assign a null value (.NULL.) to nMyvariable, issue the following commands
  in the Command window:

     store .NULL. to nMyvariable        && and press ENTER
     ? TYPE("nMyvariable")              && and press ENTER
     ? nMyvariable                      && and press ENTER

  The value N is displayed followed by .NULL.; the type of the variable did not
  change but the value did.

3. To assign a character string to the variable and check the variable type,
  issue the following commands in the Command window:

     cMyvariable="This is a String"     && and press ENTER
     ? cMyvariable                      && and press ENTER

  The screen displays the string "This is a String."

4. Issue the following command in the Command window:

     ? TYPE("cMyvariable")              && and press ENTER

  The screen displays C denoting a character type.

5. Issue the following commands in the Command window:

     STORE .NULL. TO cMyvariable        && and press ENTER
     ?TYPE("cMyvariable")               && and press ENTER

  The screen displays C to show that the type has not been changed.

Additional query words: VFoxWin

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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