Re: How to implement qsort_r

[Eric Blake <eblake at redhat dot com>]

On 12/04/2014 10:11 AM, Yaakov Selkowitz wrote:
>> My personal preference is the glibc style (the opaque argument last in
>> both qsort_r and the comparator), not the BSD style (the opaque argument
>> first in both calls),  This is because POSIX already has other
>> standardized functions in the glibc style (pthread_cleanup_push,
>> pthread_create), and none in the BSD styloe.
> 
> Generally I would agree, but wouldn't it make more sense to group
> together the arguments to compar, IOW:
> 
> void qsort_r(void *base, size_t nmemb, size_t size, void *arg, int
> (*compar)(const void *, const void *, void *));

No - I generally see code doing 'callback, opaque' and expecting a call
to callback(other args..., opaque).  What you've written here matches
neither BSD nor glibc, and does NOT preserve the pthread_create
precedent of 'callback, opaque' turning into a call to callback(...,
opaque).

BSD was at least consistent in having 'opaque, callback' turn into
'callback(opaque, ...)' (opaque always first), but as Corinna points
out, this form is not shim-able, while glibc's opaque-last is.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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