Re: fpurge now available in cygwin

[Bruno Haible]

Eric Blake wrote:
> +  /* Discard the buffered 'h', leaving position at EOF.  */
>    ASSERT (fpurge (fp) == 0);
> +  ASSERT (getc (fp) == EOF);

The file position after fpurge was not specified so far. I'm adding a check of
the file position after fpurge, not only when discarding input but also when
discarding output. The check passes on glibc, BSD systems (I tested MacOS X),
and traditional Unix systems (I tested Solaris 10).


2009-08-16  Bruno Haible  <address@hidden>

        Clarify fpurge's effect on the file position.
        * lib/stdio.in.h (fpurge): Specify the file position after fpurge.
        * tests/test-fpurge.c (main): Make a second pass for checking the file
        position.

*** lib/stdio.in.h.orig 2009-08-16 15:49:25.000000000 +0200
--- lib/stdio.in.h      2009-08-16 15:45:16.000000000 +0200
***************
*** 414,419 ****
--- 414,422 ----
  # if @REPLACE_FPURGE@ || address@hidden@
    /* Discard all pending buffered I/O data on STREAM.
       STREAM must not be wide-character oriented.
+      When discarding pending output, the file position is set back to where it
+      was before the write calls.  When discarding pending input, the file
+      position is advanced to match the end of the previously read input.
       Return 0 if successful.  Upon error, return -1 and set errno.  */
    extern int fpurge (FILE *gl_stream);
  # endif
*** tests/test-fpurge.c.orig    2009-08-16 15:49:25.000000000 +0200
--- tests/test-fpurge.c 2009-08-16 15:45:11.000000000 +0200
***************
*** 40,113 ****
  int
  main ()
  {
!   FILE *fp;
  
!   /* Create a file with some contents.  */
!   fp = fopen (TESTFILE, "w");
!   if (fp == NULL)
!     goto skip;
!   if (fwrite ("foobarsh", 1, 8, fp) < 8)
!     goto skip;
!   if (fclose (fp))
!     goto skip;
! 
!   /* The file's contents is now "foobarsh".  */
! 
!   /* Open it in read-write mode.  */
!   fp = fopen (TESTFILE, "r+");
!   if (fp == NULL)
!     goto skip;
!   if (fseek (fp, 3, SEEK_CUR))
!     goto skip;
!   if (fwrite ("g", 1, 1, fp) < 1)
!     goto skip;
!   if (fflush (fp))
!     goto skip;
!   if (fwrite ("bz", 1, 2, fp) < 2)
!     goto skip;
!   /* Discard pending write.  */
!   ASSERT (fpurge (fp) == 0);
!   ASSERT (fclose (fp) == 0);
! 
!   /* Open it in read-only mode.  */
!   fp = fopen (TESTFILE, "r");
!   if (fp == NULL)
!     goto skip;
!   {
!     char buf[8];
!     if (fread (buf, 1, 7, fp) < 7)
!       goto skip;
!     ASSERT (memcmp (buf, "foogars", 7) == 0);
!   }
!   /* Discard the buffered 'h', leaving position at EOF.  */
!   ASSERT (fpurge (fp) == 0);
!   ASSERT (getc (fp) == EOF);
!   ASSERT (fclose (fp) == 0);
! 
!   /* The file's contents is now "foogarsh".  */
! 
!   /* Ensure that purging a read does not corrupt subsequent writes.  */
!   fp = fopen (TESTFILE, "r+");
!   if (fp == NULL)
!     goto skip;
!   if (fseek (fp, -1, SEEK_END))
!     goto skip;
!   ASSERT (getc (fp) == 'h');
!   ASSERT (getc (fp) == EOF);
!   ASSERT (fpurge (fp) == 0);
!   ASSERT (putc ('!', fp) == '!');
!   ASSERT (fclose (fp) == 0);
!   fp = fopen (TESTFILE, "r");
!   if (fp == NULL)
!     goto skip;
!   {
!     char buf[10];
!     ASSERT (fread (buf, 1, 10, fp) == 9);
!     ASSERT (memcmp (buf, "foogarsh!", 9) == 0);
!   }
!   ASSERT (fclose (fp) == 0);
  
!   /* The file's contents is now "foogarsh!".  */
  
    remove (TESTFILE);
    return 0;
--- 40,134 ----
  int
  main ()
  {
!   int check_filepos;
  
!   for (check_filepos = 0; check_filepos <= 1; check_filepos++)
!     {
!       FILE *fp;
! 
!       /* Create a file with some contents.  */
!       fp = fopen (TESTFILE, "w");
!       if (fp == NULL)
!       goto skip;
!       if (fwrite ("foobarsh", 1, 8, fp) < 8)
!       goto skip;
!       if (fclose (fp))
!       goto skip;
! 
!       /* The file's contents is now "foobarsh".  */
! 
!       /* Open it in read-write mode.  */
!       fp = fopen (TESTFILE, "r+");
!       if (fp == NULL)
!       goto skip;
!       if (fseek (fp, 3, SEEK_CUR))
!       goto skip;
!       if (fwrite ("g", 1, 1, fp) < 1)
!       goto skip;
!       if (fflush (fp))
!       goto skip;
!       if (fwrite ("bz", 1, 2, fp) < 2)
!       goto skip;
!       /* Discard pending write.  */
!       ASSERT (fpurge (fp) == 0);
!       /* Verify that when discarding pending output, the file position is set
!        back to where it was before the write calls.  */
!       if (check_filepos)
!       ASSERT (ftell (fp) == 4);
!       ASSERT (fclose (fp) == 0);
! 
!       /* Open it in read-only mode.  */
!       fp = fopen (TESTFILE, "r");
!       if (fp == NULL)
!       goto skip;
!       /* Verify that the pending writes before the fpurge were really
!        discarded.  */
!       {
!       char buf[8];
!       if (fread (buf, 1, 7, fp) < 7)
!         goto skip;
!       ASSERT (memcmp (buf, "foogars", 7) == 0);
!       }
!       /* Discard the buffered 'h'.  */
!       if (check_filepos)
!       ASSERT (ftell (fp) == 7);
!       ASSERT (fpurge (fp) == 0);
!       /* Verify that when discarding pending input, the file position is
!        advanced to match the end of the previously read input.  */
!       if (check_filepos)
!       ASSERT (ftell (fp) == 8);
!       ASSERT (getc (fp) == EOF);
!       ASSERT (fclose (fp) == 0);
! 
!       /* The file's contents is now "foogarsh".  */
! 
!       /* Ensure that purging a read does not corrupt subsequent writes.  */
!       fp = fopen (TESTFILE, "r+");
!       if (fp == NULL)
!       goto skip;
!       if (fseek (fp, -1, SEEK_END))
!       goto skip;
!       ASSERT (getc (fp) == 'h');
!       ASSERT (getc (fp) == EOF);
!       if (check_filepos)
!       ASSERT (ftell (fp) == 8);
!       ASSERT (fpurge (fp) == 0);
!       if (check_filepos)
!       ASSERT (ftell (fp) == 8);
!       ASSERT (putc ('!', fp) == '!');
!       ASSERT (fclose (fp) == 0);
!       fp = fopen (TESTFILE, "r");
!       if (fp == NULL)
!       goto skip;
!       {
!       char buf[10];
!       ASSERT (fread (buf, 1, 10, fp) == 9);
!       ASSERT (memcmp (buf, "foogarsh!", 9) == 0);
!       }
!       ASSERT (fclose (fp) == 0);
  
!       /* The file's contents is now "foogarsh!".  */
!     }
  
    remove (TESTFILE);
    return 0;