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Test if a variable exists in Desktop

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  • Test if a variable exists in Desktop

    I am trying to test to see if a simple global variable exists before creating a new one in xbasic. I was trying the variable_exist() and it works perfect if answer is true but if false get an error message. After doing more research found it is not for the desktop. Then tried eval() and eval_valid() with same results. If variable exists then it will give me answer of true but if it does not exist then get an error message.

    I know I can do a work around by dim the variable in the autoexec. Is that the only way to solve my problem?

  • #2
    Re: Test if a variable exists in Desktop

    From: http://wiki.alphasoftware.com/DIM

    Note: A second DIM statement that redefines an existing variable does not cause an error. The value of the original variable is retained.
    MyNote: If you use the = option of the DIM statement. Then the = doesn't work.

    More specifically what are you trying to avoid and when are you doing this?

    Note these results.

    Code:
    dim GLOBAL mytest as C
    mytest="aa"
    ?eval_valid(mytest)
    = .F.
    ?eval_valid(var->mytest)
    = .F.
    ?eval_valid("var->mytest")
    = .T.
    ?eval_valid("var->mytesta")
    = .F.
    
    ?eval(mytest)
    ERROR: Variable "aa" not found.
    ?eval(var->mytest)
    ERROR: Variable "aa" not found.
    ?eval("mytest")
    = "aa"
    ?eval("var->mytest")
    = "aa"
    Last edited by Al Buchholz; 10-27-2015, 04:26 PM. Reason: added results section
    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

    http://www.iadn.com/images/media/iadn_member.png

    Comment


    • #3
      Re: Test if a variable exists in Desktop

      Thanks. Learned something today. I was afraid if I dim a variable that already existed I would lose the value if the variable did exist. I have now played with this in the interactive window and see I can dim all day long and the variable if it exist will keep the value that it had.

      Thanks for the quick answer Al.

      Comment


      • #4
        Re: Test if a variable exists in Desktop

        I guess I was screwing up since I was not using the quotation marks (" ")

        Dim GLOBAL mytest as c
        ?eval_valid("var->mytest")
        = .T.
        delete mytest
        ?eval_valid("var->mytest")
        = .F.

        delete mytest

        Comment


        • #5
          Re: Test if a variable exists in Desktop

          if you don't care if the variable holds any data, just use:

          delete mytest
          dim global mytest as c

          the delete {variable_name} does not pop an error if it doesn't exist. if it exists, it will delete it, if it doesn't exist, nothing happens.

          Comment


          • #6
            Re: Test if a variable exists in Desktop

            Be consistent with the scope of the variable.

            http://wiki.alphasoftware.com/~alphafiv/DELETE

            Delete needs to know the scope of the variable otherwise it assumes local.
            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

            http://www.iadn.com/images/media/iadn_member.png

            Comment


            • #7
              Re: Test if a variable exists in Desktop

              This may be a case where the interactive behaves differently.


              Code:
              dim mvar as C
              dim shared myvar as N
              dim global myvar as L
              delete myvar
              
              ? a5_list_user_vars(local_variables())
              = mvar
              ? a5_list_user_vars(session_variables())
              = profile
              ? a5_list_user_vars(global_variables())
              = myvar
              There can be only one.

              Comment


              • #8
                Re: Test if a variable exists in Desktop

                Originally posted by Al Buchholz View Post
                Be consistent with the scope of the variable.

                http://wiki.alphasoftware.com/~alphafiv/DELETE

                Delete needs to know the scope of the variable otherwise it assumes local.
                in my testing it doesn't seem to matter:

                immediate window:
                Code:
                dim global mytest as n
                dim global mytest as c
                ERROR: Variable type mismatch: variable mytest is type 'N', attempted to assign type 'C'.
                
                delete mytest
                
                dim global mytest as c

                Comment


                • #9
                  Re: Test if a variable exists in Desktop

                  ran this script with debug - got this result.

                  image of script and debug
                  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

                  http://www.iadn.com/images/media/iadn_member.png

                  Comment


                  • #10
                    Re: Test if a variable exists in Desktop

                    I guess that may be true if you dim the 3 types of variables with the same name. this is something I would never do. you could never be sure you're using the correct scope of the variable.

                    Comment


                    • #11
                      Re: Test if a variable exists in Desktop

                      Originally posted by gkeramidas View Post
                      I guess that may be true if you dim the 3 types of variables with the same name. this is something I would never do. you could never be sure you're using the correct scope of the variable.
                      Gary

                      The point is that the delete variable defaults to Local and needs to be specifically stated for Session or Global, otherwise you are deleting a Local variable not a Session or Global.
                      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

                      http://www.iadn.com/images/media/iadn_member.png

                      Comment


                      • #12
                        Re: Test if a variable exists in Desktop

                        yes, it defaults to local, but if there is only a global variable with that name, a shared variable with that name or a local variable with that name, delete myvar will delete it without expressly telling it that it's a global , shared or local variable.

                        it deleted myvar because it's the only variable named myvar. in your example, with 3 different scopes, you have to explicitly tell it which one. when there is only one, delete myvar will delete any type of variable scope.

                        if you run this code it will show you the value of the character based variable and at the end, myvar will not be listed anywhere.

                        Code:
                        delete myvar ' doesn't even pop an error when a variable by this name does not exist
                        dim global myvar as n
                        myvar = 1
                        delete myvar
                        dim global myvar as c
                        myvar = "test global"
                        showvar(myvar)
                        
                        
                        delete myvar
                        dim shared myvar as n
                        myvar = 1
                        delete myvar
                        dim shared myvar as c
                        myvar = "test shared"
                        showvar(myvar)
                        
                        delete myvar
                        dim myvar as n
                        myvar = 1
                        delete myvar
                        dim myvar as c
                        myvar = "test local"
                        showvar(myvar)
                        
                        x=a5_list_user_vars(local_variables())
                        y=a5_list_user_vars(session_variables())
                        z =a5_list_user_vars(global_variables())
                        
                        showvar(x + crlf() + y + crlf() + z)

                        Comment

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