From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/5936 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: fgets behaviour after eof Date: Wed, 27 Aug 2014 12:52:45 -0400 Message-ID: <20140827165245.GQ12888@brightrain.aerifal.cx> References: <20140827111620.GY22308@port70.net> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1409158385 19004 80.91.229.3 (27 Aug 2014 16:53:05 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 27 Aug 2014 16:53:05 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-5943-gllmg-musl=m.gmane.org@lists.openwall.com Wed Aug 27 18:52:58 2014 Return-path: Envelope-to: gllmg-musl@plane.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1XMgSw-0000yO-5p for gllmg-musl@plane.gmane.org; Wed, 27 Aug 2014 18:52:58 +0200 Original-Received: (qmail 7893 invoked by uid 550); 27 Aug 2014 16:52:57 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 7885 invoked from network); 27 Aug 2014 16:52:57 -0000 Content-Disposition: inline In-Reply-To: <20140827111620.GY22308@port70.net> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:5936 Archived-At: On Wed, Aug 27, 2014 at 01:16:20PM +0200, Szabolcs Nagy wrote: > the C standard requires that > > "If end-of-file is encountered and no characters have been read into the > array, the contents of the array remain unchanged and a null pointer is > returned. If a read error occurs during the operation, the array contents > are indeterminate and a null pointer is returned." > > but musl's fgets always terminates the buffer with \0 even after EOF, > this is easy to fix: > > - *p = 0; > + if (s) *p = 0; This is wrong and should be fixed, yes. > However the behaviour of fgets(s, 1, f) is unclear if feof(f) is true, > in this case nothing is read so fgets cannot "encounter" end-of-file, > so it may set s[0]=0 and return s or it could check feof and return 0. > (glibc does not check feof) This is a known WONTFIX bug in glibc from the Drepper era. Remember, all stdio read operations are defined in terms of fgetc, for which it is specified: "Upon successful completion, fgetc() shall return the next byte from the input stream pointed to by stream. If the end-of-file indicator ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ for the stream is set, or if the stream is at end-of-file, the ^^^^^^^^^^^^^^^^^^^^^ end-of-file indicator for the stream shall be set and fgetc() shall return EOF." Thus, fgets encounters EOF from fgetc. Rich