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Message-ID: <41BDF3A0.6020909@redhat.com>
Date: Mon, 13 Dec 2004 14:55:12 -0500
From: Jeff Johnston <jjohnstn AT redhat DOT com>
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To: Peter Astrand <astrand AT lysator DOT liu DOT se>
Cc: cygwin AT cygwin DOT com, newlib AT sources DOT redhat DOT com
Subject: Re: short fread(), but no ferror/feof
References: <Pine DOT GSO DOT 4 DOT 51L2 DOT 0412051701370 DOT 21199 AT koeberg DOT lysator DOT liu DOT se> <Pine DOT GSO DOT 4 DOT 51L2 DOT 0412112312480 DOT 19131 AT koeberg DOT lysator DOT liu DOT se>
In-Reply-To: <Pine.GSO.4.51L2.0412112312480.19131@koeberg.lysator.liu.se>
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Peter Astrand wrote:
> Dave Korn wrote:
> 
> 
>> The fix and the problem Peter is seeing are orthogonal.
>>
>> The fix referred to above fixes this problem:
>>
>>http://sources.redhat.com/ml/newlib/2004/msg00478.html
>>"Hence, one can see that fread() in unbuffered mode always returns the
>>specified count instead of the number of elements actually read."
>>
>> That is why, as Peter has observed, fread() returns the number of
>>elements
>>actually read.  Without the patch, it would have been returning the entire
>>number requested, which would have been even wronger.
> 
> 
> Ah, thanks for clarifying this.
> 
> 
> 
>> However Peter's problem is that when fread() does a partial read, it doesn't
>>set either the EOF mark or the error indication on the file stream.  A strict
>>reading of the fread() specification suggests that it should have set one of
>>those.
> 
> 
> IMO, there's no room for intepretation in this situation: As I stated
> in my original post, IEEE Std 1003.1 is very clear:
> 
> "fread() shall return the number of elements successfully read which is
> less than nitems only if a read error or end-of-file is encountered."
>

Where in the POSIX standard did you find that above line?  I could not locate it 
in mine.  The line above is in SUSV3.  ANSI and C99 are more relaxed and simply 
state that the number of elements returned may be less than asked if EOF or an 
error has occurred.

Regardless, the behavior is wrong.  The same test on a buffered file yields the EOF.

I have posted a patch.

-- Jeff J.


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