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Is it possible to Gosub to a variable?

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  • Is it possible to Gosub to a variable?

    I'd like to GOSUB to a variable if this is possible. I've played around with STRPTR but without success. Any help would be appreciated.
    DIM point AS DWORD
    XX$=Air_Injector

    point = STRPTR(XX$)
    GOSUB DWORD point


    Air_Injector:
    'code
    RETURN

  • #2
    To a (numeric) variable, yes; to a string, no (not directly).
    This works:

    Code:
    FUNCTION PBMAIN
    
      DIM p AS LONG
      
      p = CODEPTR(MyLabel)
      GOSUB DWORD p
      
      WAITKEY$
      EXIT FUNCTION       
           
    MyLabel:
      PRINT "MyLabel reached!"
      RETURN       
           
    END FUNCTION
    If you want to use a string to identify a target, just organize whatever kind of list you prefer to associate a string to a number.

    Bye!
    -- The universe tends toward maximum irony. Don't push it.

    File Extension Seeker - Metasearch engine for file extensions / file types
    Online TrID file identifier | TrIDLib - Identify thousands of file formats

    Comment


    • #3
      Code:
       ON var GOSUB x, y, z...
      ???

      Let'ts enance that a little bit...
      Original code:
      Code:
      XX$=Air_Injector
      point = STRPTR(XX$)
      GOSUB DWORD point
      How about
      Code:
         ON SWITCH (XX$ = "Air_Injector", 1, _ 
                           XX$="Steam_shovel", 2, _
                           XX$ = "Dump_truck", 3) _ 
               GOSUB air_injector, steam_shovel, dump_truck
      Kind of the long way, but hey, it looks pretty cool.
      Last edited by Michael Mattias; 15 Apr 2008, 04:57 PM.
      Michael Mattias
      Tal Systems Inc. (retired)
      Racine WI USA
      [email protected]
      http://www.talsystems.com

      Comment


      • #4
        Simple answer is no
        Gosub, Function, Sub must point to actual code.
        You can gosub to code as the result of a test on a variable (and the address of the code can be stored in a dword) but programs can only run code. If your sting contained binary machine code but not text

        Comment


        • #5
          Bill,

          Have a look at ON GOSUB. It allows you to use it with "line numbers".
          C'ya
          Don

          http://www.ImagesBy.me

          Comment


          • #6
            Keeping in mind that the subroutine must be located within the confines of the SUB/FUNCTION that is calling it.

            You cannot GOSUB outside the boundaries of SUB/FUNCTION <-> END SUB/FUNCTION.

            That little detail caused me a lot of headscratching when I transitioned from PB/DOS to CC.
            There are no atheists in a fox hole or the morning of a math test.
            If my flag offends you, I'll help you pack.

            Comment


            • #7
              Given that you can get a pointer to code, I can't see why you should not be able to copy code into a string and execute it. However, there is a constraint on GOSUB that the label should be within the current block, I'm not sure how, or if, the generated code enforces this if you GOSUB to a CODEPTR. Why not give it a try?
              Last edited by Chris Holbrook; 17 Apr 2008, 07:38 AM.

              Comment


              • #8
                Given that you can get a pointer to code, I can't see why you should not be able to copy code into a string and execute it.
                ????

                If you can get a pointer to the code, you can CALL it, GOTO it or GOSUB to it using the DWORD option provided by the compiler for all three verbs. Why bother getting its length, copying it into a string after allocating virtual memory with execute permissions and all that stuff?
                Michael Mattias
                Tal Systems Inc. (retired)
                Racine WI USA
                [email protected]
                http://www.talsystems.com

                Comment


                • #9
                  Originally posted by Michael Mattias View Post
                  Why bother...?
                  quite.

                  Comment


                  • #10
                    Air_Injector is a label

                    I was able to get this code working;


                    XX$= STR$ ( CODEPTR (Air_Injector) )
                    point = VAL(XX$)
                    GOSUB DWORD point

                    Your original code of XX$ = Air_Injector elicited an error presumably
                    because Air_injector is a label and XX$ is a string variable .

                    The three lines of code above could be written as ;

                    GOSUB DWORD CODEPTR(Air_Injector)

                    The main advantage of the GOSUB DWORD implementation is that Air_Injector need not be within the scope of the calling function; where as
                    GOSUB Air_Injector
                    must be within the scope, as well as various forms of the
                    '
                    On var GOSUB Air_Injector implementation

                    Comment


                    • #11
                      The main advantage of the GOSUB DWORD implementation is that Air_Injector need not be within the scope of the calling function
                      Some might consider that a dis-advantage, as it is explicitly not supported; from the help file (8.03) under GOSUB:
                      All labels and line numbers are private. You cannot GOSUB to a label outside of the current Sub or Function.
                      That is, don't be surprised if this fails miserably in a new release of the compiler.

                      Sounds to me like whatever is at the label Air_Injector should be re-written as a separate procedure so it may be called from any other procedures.
                      Michael Mattias
                      Tal Systems Inc. (retired)
                      Racine WI USA
                      [email protected]
                      http://www.talsystems.com

                      Comment

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