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From: Chalmers@europarc.xerox.com (Matthew Chalmers)
Newsgroups: comp.lang.modula3
Subject: oddness with 2-d arrays
Message-ID: <8bc6zicB0Tlj05F1Y8@sparky.EuroPARC.Xerox.COM>
Date: 25 Jan 91 17:50:38 GMT
Lines: 93
To: m3
Cc: Matthew Chalmers <Chalmers@europarc.xerox.com>

Hi -

Concatenated below are a number of files which collectively show
something I don't understand with passing arrays to a procedure in a
module. The difference seems to be whether arrays are passed as open or
of fixed length (c.f. foo.proc1 and foo.proc2). The output of the
collected code is just below, and this shows the wierdness: only 3
longreals copied across(?) instead of 6.

Main:
 1 2
 3 4
 9 8

proc1
 1 2
 3 4
 9 8

proc2
 1 2
 3 4.55779D-309
 4.24399D-314 1.37939D-318

I had expected proc2 to output the same thing as proc1.

Regards,

Matthew Chalmers

(*-------------------- cut here -------------------- *)


INTERFACE foo;

TYPE 
  TwoVec   = ARRAY [0..1] OF LONGREAL;

PROCEDURE proc1 (p : ARRAY [0..2] OF TwoVec); 
PROCEDURE proc2 (p : ARRAY OF TwoVec); 

END foo.

MODULE foo;
IMPORT Wr, Stdio, Fmt;

PROCEDURE proc1 (p : ARRAY [0..2] OF TwoVec) =
BEGIN
  Wr.PutText(Stdio.stdout,"\nproc1\n");
  FOR i := 0 TO NUMBER(p)-1 DO
    Wr.PutText(Stdio.stdout," " & Fmt.LongReal(p[i][0]));
    Wr.PutText(Stdio.stdout," " & Fmt.LongReal(p[i][1]) & "\n");
  END;
END proc1;

PROCEDURE proc2 (p : ARRAY OF TwoVec) =
BEGIN
  Wr.PutText(Stdio.stdout,"\nproc2\n");
  FOR i := 0 TO NUMBER(p)-1 DO
    Wr.PutText(Stdio.stdout," " & Fmt.LongReal(p[i][0]));
    Wr.PutText(Stdio.stdout," " & Fmt.LongReal(p[i][1]) & "\n");
  END;
END proc2;

BEGIN
END foo.
       

MODULE Main;
IMPORT Wr, Stdio, Fmt;
IMPORT foo;

VAR points : ARRAY [0..2] OF foo.TwoVec;
VAR x, y : LONGREAL;
BEGIN
  x := 1.0d0;
  y := 2.0d0;
  Wr.PutText(Stdio.stdout, "Main:\n");
  FOR i := 0 TO 2 DO
    points[i][0] := x;
    points[i][1] := y;

    Wr.PutText(Stdio.stdout, " " & Fmt.LongReal(x));
    Wr.PutText(Stdio.stdout, " " & Fmt.LongReal(y) & "\n");

    x := x * 3.0d0;
    y := y * 2.0d0;
  END;

  foo.proc1 (points);
  foo.proc2 (points);

END Main.