Xref: utzoo comp.os.vms:5859 comp.lang.pascal:847
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From: cfchiesa@bsu-cs.UUCP (Christopher Chiesa)
Newsgroups: comp.os.vms,comp.lang.pascal
Subject: Re: Quoted string parameters in VAX Pascal?
Message-ID: <2812@bsu-cs.UUCP>
Date: 29 Apr 88 22:06:32 GMT
References: <Apr.29.15.09.31.1988.23840@elbereth.rutgers.edu>
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 73
Summary: Something to try

In article <Apr.29.15.09.31.1988.23840@elbereth.rutgers.edu>, elkins@elbereth.rutgers.edu (George Elkins) writes:
> 
> Is there a way in VAX Pascal to define a procedure that will take
> a variable length quoted string as a parameter?  What I would like
> to do is imitate the variable length quoted string parameter behavior
> of the WRITE and WRITELN procedures, although this is not possible
> for user-written procedures in STANDARD Pascal.  I want the quoted
> string parameter to be within the argument list itself, as in the
> WRITELN procedure.  I am trying to avoid assigning the string to an
> arbitrarily long fixed-length packed array and passing the Pascal
> identifier for the array and the integer length of the string.
> 
> Example of what I want to do:
> 
>      foo('This is a string of any length');  {User-written procedure foo}
> 
> Examples of what I am avoiding:
> 
>      foo(PackedArrayName, StringLength);  {Packed array and string length}
> or
>      foo(String.Body, String.Length);  {Record with packed array and integer}
> 
> Is this possible or conceivable in VAX Pascal?  (I'll admit that I haven't
> consulted the documentation.  I don't have easy access to it.)
> 
> George Elkins

When in doubt, use a RECORD.  One hitch with that is that you usually can't
pass a RECORD data type as a parameter, but you can get around THAT by pass-
ing a POINTER to the record you're after.

For variable-length strings, you'll still have to work within SOME maximum-
length limit, but in general you'd do something like this:

TYPE
      vstring: ^vrec;

      vrec: RECORD
           body   : PACKED ARRAY [1..maxstring] OF char;
           length : INTEGER;
        END;

PROCEDURE FakeWriteln (VAR s: vstring);
  BEGIN
   (* Assorted manipulations of the string having body s^.body, of which 
      the first s^.length characters are valid. *)
   .
   .
   .
  END;

Now, it just so happens that the folks at DEC anticipated this, and built in
a datatype you may be aware of but haven't mentioned:

       VARYING [...] OF char;

This creates an "implicit record" type, containing the fields "body" and 
"length" pretty much as I declared 'em above for (semi-) standard Pascal.

In Vax Pascal, anyway, "write" and "read" and "writeln" and so on, will oper-
ate quite happily on these variable-length strings.

You can pass them to system routines, also, using either the "%desc" or 
"%stdesc" passing-mechanism specifiers (I forget which is for VARYING strings
and which is for PACKED strings; try 'em and use whatever works... :-)  )

Hope this is of use to you; feel free to e-mail for clarification.

Chris Chiesa

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