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From: mwizard@eecs.cs.pdx.edu (Craig Nelson)
Newsgroups: comp.lang.pascal
Subject: Re: Pointers to procedures
Message-ID: <2301@pdxgate.UUCP>
Date: 10 Apr 91 08:44:02 GMT
References: <26505@adm.brl.mil>
Sender: news@pdxgate.UUCP
Lines: 108

CDCKAB%EMUVM1.BITNET@cunyvm.cuny.edu ( Karl Brendel) writes:

>In article <9104081439.aa02828@VGR.BRL.MIL>, 209507097@ucis.vill.edu
>  (MCREE, JAMES F) wrote:

>>        I been following the thread of calling procedures by
>>pointers with a lot of interest recently.  Mostly because I have an
>>application that is just begging for a solution like that.  However,
>>the discussion and samples that I have seen (including those in the
>>manual) deal with hardcoding procedure names into the program.  (ie.
>>Proc[i] := Do_It_Procedure)  Is there a way of doing what my
>>syntactically incorrect program below is trying to do?
>>
>>Program Call_A_Variable_Procedure (Input,Output);
>>.
>>Var
>>    Proc_Name : Procedure;
>>.
>>.
>>Assorted necessary delcarations
>>.
>>Begin
>>.
>>.
>>Assorted code statements
>>.
>>.
>>Write ('Enter the name of a procedure to run: ');
>>Readln (Proc_Name);
>>Proc_Name;
>>.
>>.
>>End.
>>
>>
>>This is an example of a user-specified call to a procedure.  The
>>user specifies the procedure directly though.  Can this be done?

>It isn't really apparent (to me) that your application is truly
>"begging for a solution like [pointers to procedures]". Why can you
>not just use a series of IF statements for your purpose?

>        Proc_Name := stUpCase(Proc_Name);
>        IF Proc_Name = 'PROC_A' THEN Proc_A
>        ELSE IF Proc_Name = 'PROC_B' THEN ProcB
>        etc....


	How about this:

{$F+}
procedure proc1;
begin
  writeln('In Proc1');
end;

procedure proc2;
begin
  writeln('In Proc2');
end;

procedure proc3;
begin
  writeln('In Proc3');
end;



Const 

    NumProcedures = 3;

Type 

     ProcString = String[10];
     ProcRec = Record
		Name:PString;
		Proc:Procedure;
	       end;	


Const
     MyProcedures : Array[1..NumProcedures] of ProcRec = (
			(Name:'PROC1';Proc:proc1),
			(Name:'PROC2';Proc:proc2),
			(Name:'PROC3';Proc:proc3));
	


	With this kind of setup you should be able to have a function that
runs the procedure desired if found from the input line.  For instance, if
the function returned and index if the proper procedure was found, and 0 on
an error, then

	i:= FindProcedure(ReadString);
        if (i>0) then MyProcedures[i].Proc
	else writeln('No such procedure');


	Am I missing something or will this work ?  Should.... Looks like it
	will.

Cheers!

 []====================================================================[]
 || Craig R. Nelson                | CCSofD Software Inc.              ||
 || Programmer                     | Beaverton, OR, 97005              ||
 || mwizard@eecs.ee.pdx.edu        | (unlisted on the net)             ||