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Date: Mon, 23 Jul 2012 23:34:09 -0400
From: pete <pfiland@mindspring.com>
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Subject: Re: qsort man page
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Bill Cunningham wrote:
> 
> This is from the qsort man page. I don't quite understand why there is
> a comment here saying that arguments to this generic function to pass
> to qsort is a pointer to pointer.
> It looks to me like cmpstringp takes
> a generic pointer. Not pointer to pointer. Why does the comment say
> pointer to pointer? 

Because the argument that qsort will pass to cmpstringp,
when qsort calls cmpstringp,
is a pointer to a pointer.

> This is confusing me also with the strcmp
> parameters which are cast as a pointer to pointer and dereferenced.

The argument that qsort will pass to cmpstringp,
when qsort calls cmpstringp,
is a pointer to a pointer.

> static int
> cmpstringp(const void *p1, const void *p2)
> {
>     /* The actual arguments to this function are "pointers to
>        pointers to char", but strcmp(3) arguments are "pointers
>        to char", hence the following cast plus dereference */
>     return strcmp(* (char * const *) p1, * (char * const *) p2);
> }



-- 
pete