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From: carroll@s.cs.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: File descriptors and streams and co
Message-ID: <207600018@s.cs.uiuc.edu>
Date: 16 Apr 89 23:32:00 GMT
References: <1743@leah.Albany.Edu>
Lines: 24
Nf-ID: #R:leah.Albany.Edu:1743:s.cs.uiuc.edu:207600018:000:1068
Nf-From: s.cs.uiuc.edu!carroll    Apr 16 18:32:00 1989


I must be missing something - given that
FILE *my_file;
has been properly set up (with fopen(), no errors, etc.), why can't you
switch stdin by having another variable
FILE *tmp;
and doing
tmp = stdin; stdin = my_file;

'stdin' is declared as a pointer, and so setting the pointer to point at
a different FILE I/O block should cause routines that use it to read from
that file instead. You can then restore by
stdin = tmp;

Mr. Salz indicated that things are more complex than this. Is this because
of library routines with file descriptor 0 wired in, or because file info
is kept in places other than the FILE I/O block stdin points to? While
this might not work in all cases, it seems to me it should in the original
case, if twiddling the file descriptor in the block works. (i.e., it must
not be hard-wired and must look in the FILE I/O block for things).

Alan M. Carroll                "And then you say,
carroll@s.cs.uiuc.edu           We have the Moon, so now the Stars..."  - YES
CS Grad / U of Ill @ Urbana    ...{ucbvax,pur-ee,convex}!s.cs.uiuc.edu!carroll