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array and null values

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  • array and null values

    I'm using the following xbasic to populate an array from a table. The field example below named 'box_height' is a numeric field with a null value in the table (blank).

    Look at the results of several interactive window expressions. The first expression indicates the value is 0. The second says it is not null, but then the last two expressions indicate the value is NOT 0. What's going on?

    filter = ""
    dim content[1] as p
    content.clear()
    content.initialize_from_table("content",filter)

    ?content[1].box_height
    = 0

    ?content[1].box_height = null_value()
    = .F.

    ?content[1].box_height > 0
    = .T.

    ?content[1].box_height = 0
    = .F.
    Steve Wood
    Join the ALPHA DEVELOPERS NETWORK
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  • #2
    Re: array and null values

    Can't pinpoint the links but there have been several discussions of null values and the dbf format. The gist was that the concept of a null value doesn't exist in the dbf specifications. An uninitialized numeric field will evaluate to zero or a VLN depending on the situation.

    Code:
    tbl = table.open("sometablename")
    ? tbl.num
    = 0
    There can be only one.

    Comment


    • #3
      Re: array and null values

      Steve ... dont know if this helps, but in help doc it states ...

      Note : Numeric variables are a special case. You cannot use NULL_VALUE() with a numeric variable. However, if you have a numeric field, you can set the field value to NULL_VALUE().

      Looks like your setting the array variable to null_value ...

      Glenn

      Comment


      • #4
        Re: array and null values

        I think I participated in some of those discussions.

        I forced my numeric fields to be zero as a default. So the value is either a zero or a user-entered value. Here are the array results when the value is a zero rather than 'blank':

        ?content[1].box_height
        = 0

        ?content[1].box_height = null_value()
        = .T.

        ?content[1].box_height > 0
        = .F.

        ?content[1].box_height = 0
        = .T.
        Steve Wood
        Join the ALPHA DEVELOPERS NETWORK
        There is no Cloud. It's just someone else's computer.
        Web - Mobile - Hosting - Products - Frameworks - Developer Resources
        AlphaToGo | IADN (100% Alpha Anywhere Websites)

        Comment


        • #5
          Re: array and null values

          woops ... sorry steve ... your testing for value not assigning ....

          So was the question .... why is the field not testing for Null when it looks like it should be? and your work-around is to force numeric 0 to the field?

          Glenn

          Comment


          • #6
            Re: array and null values

            No longer sure what my question was. I switched gears and changed my numeric fields in to character fields and added validation to ensure only positive integers are added. I need "0" to mean 'has a value of zero' and blank to mean 'no value is assigned'.
            Steve Wood
            Join the ALPHA DEVELOPERS NETWORK
            There is no Cloud. It's just someone else's computer.
            Web - Mobile - Hosting - Products - Frameworks - Developer Resources
            AlphaToGo | IADN (100% Alpha Anywhere Websites)

            Comment


            • #7
              Re: array and null values

              It is amazing how transforming how you look at a problem can create a totally different yet effective path to a solution.

              I think all of the standing on my head to get a different perspective has contributed to hair loss. It can't be the hair pulling frustration......

              Steve - thanks for sharing.
              Al Buchholz
              Bookwood Systems, LTD
              Weekly QReportBuilder Webinars Thursday 1 pm CST

              Occam's Razor - KISS
              Normalize till it hurts - De-normalize till it works.
              Advice offered and questions asked in the spirit of learning how to fish is better than someone giving you a fish.
              When we triage a problem it is much easier to read sample systems than to read a mind.
              "Make it as simple as possible, but not simpler."
              Albert Einstein

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