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Re: new module 'freadseek'
- From: Eric Blake <ebb9 at byu dot net>
- To: Bruno Haible <bruno at clisp dot org>
- Cc: bug-gnulib at gnu dot org, newlib at sources dot redhat dot com
- Date: Sat, 01 Mar 2008 13:36:10 -0700
- Subject: Re: new module 'freadseek'
- References: <200802291029.20111.bruno@clisp.org> <47C9960E.4010008@byu.net>
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According to Eric Blake on 3/1/2008 10:44 AM:
|
| Somehow, the tweaks you did to the raw _fp to account for the 1-byte
| readahead buffer from the arbitrary ungetc trip up the subsequent fseek.
| I'm in the process of compiling a debug version of cygwin to try to find
| out more details why cygwin's fseek failed, but it may take a while.
On further investigation, I think this is a true bug in newlib's stdio,
and not in your code. This simpler program fails some of the time, but
not if there was a previous ftell:
$ cat foo.c
#include <stdio.h>
#include <stdlib.h>
int
main (int argc, char* argv[])
{
~ int i1, i2;
~ if (argc > 1)
~ {
~ i2 = ftell (stdin);
~ printf ("i2=%d\n", i2);
~ }
~ /* Test behaviour after arbitrary ungetc. */
~ fgetc (stdin);
~ if (argc > 1)
~ {
~ i2 = ftell (stdin);
~ printf ("i2=%d\n", i2);
~ }
~ ungetc ('@', stdin);
~ if (argc > 1)
~ {
~ i2 = ftell (stdin);
~ printf ("i2=%d\n", i2);
~ }
~ i1 = fseek (stdin, 2, SEEK_CUR);
~ i2 = ftell (stdin);
~ printf ("i1=%d i2=%d\n", i1, i2);
~ return 0;
}
$ ./foo < foo.c
i1=-1 i2=-536
$ ./foo a < foo.c
i2=0
i2=1
i2=0
i1=0 i2=2
- --
Don't work too hard, make some time for fun as well!
Eric Blake ebb9@byu.net
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