[gfortran] Stop rewind deleting files.

[Paul Brook]

A write to a sequential assess file followed by tow rewind statements would 
truncate the file to zero length.The fix seems to be to put the unit into 
read mode after a rewind statement.

Tested on i686-linux.
Applied to mainline.

Paul

2004-08-27  Paul Brook  <paul@codesourcery.com>

	* io/rewind.c (st_rewind): Reset unit to read mode.
testsuite/
	* gfortran.dg/rewind_1.f90: New test.

Index: rewind.c
===================================================================
RCS file: /var/cvsroot/gcc-cvs/gcc/libgfortran/io/rewind.c,v
retrieving revision 1.4
diff -u -p -r1.4 rewind.c
--- rewind.c	27 Aug 2004 07:59:30 -0000	1.4
+++ rewind.c	27 Aug 2004 13:24:21 -0000
@@ -40,8 +40,13 @@ st_rewind (void)
 			"Cannot REWIND a file opened for DIRECT access");
       else
 	{
+	  /* If we have been writing to the file, the last written record
+	     is the last record in the file, so trincate the file now.
+	     Reset to read mode so two consecutive rewind statements
+	     don't delete the file contents.  */
           if (u->mode==WRITING)
             struncate(u->s);
+	  u->mode = READING;
 	  u->last_record = 0;
 	  if (sseek (u->s, 0) == FAILURE)
 	    generate_error (ERROR_OS, NULL);
-------------- next part --------------
! { dg-do run }
! Check that rewind doesn't delete a file.
! Writing to the file truncates it at the end of the current record.  Out
! IO library was defering the actual truncation until the file was rewound.
! A second rewind would then (incorrectly) think the file had just been
! written to, and truncate the file to zero length.
program foo
  character*11 s
  open(unit=11, status="SCRATCH")
  write(11, '(a11)') "Hello World"
  rewind(11)
  rewind(11)
  s = ""
  read(11, '(a11)') s
  close(11)
  if (s .ne. "Hello World") call abort
end program