From: Erik Max Francis <max AT alcyone DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: fread/fwite return value
Date: Thu, 17 Jul 1997 08:30:34 -0700
Organization: Alcyone Systems
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Message-ID: <33CE3A9A.295543E2@alcyone.com>
References: <199707161302 DOT PAA20053 AT free DOT polbox DOT pl>
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To: djgpp AT delorie DOT com
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heretic AT polbox DOT com wrote:

> I've noticed a kind of anomaly while writing a program using
> fwrite/fread functions. First take a look at library reference:
> 
> size_t  fread(void *_ptr, size_t _size, size_t _nelem, FILE *_stream);
> 
> (...)
> 
> Return value
> ============
> The number of items of size SIZE read, or -1 on error.

The library reference is wrong, and fread's return type being unsigned is
consistent with its return type.  From ANSI C, 7.9.8.1:

    size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);

    The fread function returns the number of elements successfully read,
    which may be less than `nmemb' if a read error or end-of-file is
    encountered.

That is, it always returns the number of elements (not number of bytes!)
successfully read; an error indication would not be a negative number, but
rather less than the number of elements you asked it to read.

fwrite is analogous with respect to this behavior.

That is, 

    Block *data;
    int elements;

    /* ... */

    if (fread(block, sizeof(Data), elements, file) != elements)
        /* error condition ... */

-- 
       Erik Max Francis, &tSftDotIotE / email / max AT alcyone DOT com
                     Alcyone Systems /   web / http://www.alcyone.com/max/
San Jose, California, United States /  icbm / 37 20 07 N  121 53 38 W
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