Re: fread, fwrite with size 0

[Rich Felker <dalias@libc.org>]

On Wed, Feb 03, 2016 at 09:53:21AM +0100, hombre wrote:
> Hello,
> 
> I think that fread and fwrite does not return 0 when parameter size
> is 0 (when nmemb is 0, it does).
> Clib spec says: If size or nmemb is zero, fread/fwrite returns zero
> 
> I did the following changes to make it work:
> 
> fread:
> from
>     return nmemb;
> to
>     return len == 0 ? 0 : nmemb;
> 
> fwrite:
> from
>     return k == l ? nmemb : k / size;
> to
>     if (l == 0)
>         return 0;
>     else
>         return k == l ? nmemb : k / size;
> 
> Regards,
> Erwin

Thanks. Sadly the POSIX version of the text is contradictory on this:

"Upon successful completion, 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. If size or nitems is 0, fread()
shall return 0 and the contents of the array and the state of the
stream remain unchanged."

First it says that the return value can be less than nitems only if an
error of EOF happens, but then it gives another way the return value
can be less than nitems (if size is 0).

Fortunately the ISO C text is not so broken and agrees with you:

"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. If size or nmemb is zero, fread returns zero and the
contents of the array and the state of the stream remain unchanged."

There's another issue I want to fix here too, but I might do it in two
commits. Thanks for the report.

Rich