Date: Wed, 27 Aug 2014 12:52:45 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: fgets behaviour after eof 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 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
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