Newsgroups: comp.lang.pascal
Path: utzoo!utgpu!watserv1!watmath!dmurdoch
From: dmurdoch@watmath.waterloo.edu (Duncan Murdoch)
Subject: Re: Pointers to procedures
Message-ID: <1991Apr8.222045.8757@watmath.waterloo.edu>
Organization: University of Waterloo
References: <26486@adm.brl.mil>
Date: Mon, 8 Apr 1991 22:20:45 GMT
Lines: 54

In article <26486@adm.brl.mil> 209507097@ucis.vill.edu (MCREE, JAMES F) writes:
>
>	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?
...
>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?

The closest thing to what you've got there would be to create an array of
procedure variables, and a corresponding array of names.  Then when the user
enters a name, search through the name array for a match, and call the
corresponding procedure.

For example:

 var
   procs : array[1..2] of procedure;
   names : array[1..2] of string[8];
   name  : string[8];
   i     : integer;
 begin

   { In TP 6, these assignments could all be done in a Const declaration }

   procs[1] := add;
   names[1] := 'ADD';
   procs[2] := subtract;
   names[2] := 'SUBTRACT';

   readln(name);
   i := 1;
   while (i <= 2) and (names[i] <> name) do
     inc(i);
   if i <= 2 then
     procs[i];
  end;

I hope this helps.

Duncan Murdoch
dmurdoch@watstat.waterloo.edu (when it gets fixed)
dmurdoch@watmath.waterloo.edu (temporarily)