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From: dpaulso@relay.nswc.navy.mil (Dave Paulson)
Newsgroups: comp.unix.questions
Subject: "temporarily" redirecting stdin
Keywords: redirect, stdin
Message-ID: <1989Dec14.185745.7465@relay.nswc.navy.mil>
Date: 14 Dec 89 18:57:45 GMT
Reply-To: dpaulso@ark1.nswc.navy.mil (Dave Paulson)
Distribution: usa
Organization: Naval Surface Warfare Center, Dahlgren, VA
Lines: 22

i have a program which wants to initialize itself by reading in a
configuration file.  a lex/yacc scanner/parser pair will handle the
reading of the config file.  now, the scanner that lex generates
gathers its tokens from stdin (a behavior i want to retain),
but i'll need to use stdin for my own purposes after the
initialization is complete.   

what i propose to do is summarized in the following pseudocode:

	stdin_save = dup(fileno(stdin));  /* stdin_save is an int */
	freopen("config.file","r",stdin); /* connect stdin to the config file*/
	yyparse();			  /* works ok, input comes from file */
	close(fileno(stdin));		  /* free stdin descriptor */
	dup(stdin_save);		  /* restore old stdin */
	
this doesn't work.  after the second dup(), reading stdin results
in EOF.  what have i overlooked?


-- 
Dave Paulson			Synetics / Naval Surface Warfare Center
dpaulso@relay.nswc.navy.mil	voice:	 (703) 663-2137