Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!sun-spots-request
From: frist@ccu.umanitoba.ca
Newsgroups: comp.sys.sun
Subject: Re: SUN Pascal: Determining if a file exists before opening
Keywords: SunOS
Message-ID: <5982@brazos.Rice.edu>
Date: 21 Mar 90 17:42:00 GMT
Sender: root@rice.edu
Organization: Sun-Spots
Lines: 47
Approved: Sun-Spots@rice.edu
X-Refs:  Original: v9n88
X-Sun-Spots-Digest: Volume 9, Issue 93, message 1

Last week, I posted the question 

   In SUN Pascal, how do you test to see if a file exists, before 'reset'ting
   or 'rewrite'ing that file?

Many of the replies suggested calling the c access() procedure from
Pascal, while others sent c subroutines, or ideas for c subroutines, that
could be compiled separately and linked by the pc command.  Below is what
I think is the simplest solution. Thanks a lot to all who replied to my
query.

const  MAXLINE= 132;
type   (* LINE simulates dynamic character strings in standard Pascal *)
       CHARARRAY = packed array[1..MAXLINE] of char;
       LINE = record
                STR:CHARARRAY;
                LEN:integer
                end;

(* The c function access is found in sys/file.h. access must be declared in
   the outermost scope of the Pascal program. See access (2) manual pages *)
  function access(PATH:CHARARRAY; MODE:integer):integer; external c;

  (* The following function may appear in any scope: *)
  (* - - - - - - - - - - - - - - - - - - - - - - - - - - - *)
  (* =true if file exists, =false if it doesn't *)
  (* A comparable procedure is provided with ATT System V Pascal *)
  (* A special thank you to Mark Foster, CIS Rearch Computing, Univ. of Penn.
     and Glenn Gribble of Synaptics Inc. for showing me how to use access()
     within Pascal programs. B.F. *)
  function EXISTS(FILENAME:LINE):boolean;
    const F_OK=0; (* checks if file exists *)
    begin (* EXISTS *)
      with FILENAME do begin
        STR[LEN+1]:=chr(0); (* c strings terminate with null *)
        if access(STR,F_OK)=-1 then EXISTS:=false
        else  EXISTS:=true
        end (* with FILENAME *)
    end; (* EXISTS *)

Brian Fristensky                           frist@ccu.umanitoba.ca
Assistant Professor
Dept. of Plant Science
University of Manitoba
Winnipeg, MB R3T 2N2  CANADA
Office phone:                              204-474-6085
FAX:                                       204-275-5128