🚀 go-pugleaf

In article <4iokop$h4p@lyra.csx.cam.ac.uk>
           jkb@mrc-lmb.cam.ac.uk "James Bonfield" writes:

> Are there any limitations on what the sort function passed over to qsort can
> do or return? I know it's meant to return < 0, 0 or > 0 for the various
> compare operations, but which you return is purely up to your own comparison
> system.
> 

[snip]

> static int sort_func(const void *pa, const void *pb)
> {
>     const int *a = (int *)pa;
>     const int *b = (int *)pb;
> 
>     return *a > *b;
>
> }

You need a function which returns "an integer less than, equal to, or
greater than zero if the first argument is considered to be respectively
less than, equal to, or greater than the second" [ ANSI/ISO 9899-1990
7.10.5.2].

sort_funct returns 0, 0, and 1, respectively for the 3 cases enumerated.

Brevity is satisfied by:
     return *a < *b ? -1 : *a > *b;

You may find that conformity to the interface is better shown by:
     return (*a < *b) ? -1 : ((*a == *b) ? 0 : 1);

I think I prefer to avoid the multiple dereferencing with:

static int sort_func(const void *pa, const void *pb)
{
    int a = *(const int *)pa;
    int b = *(const int *)pb;

    return a < b ? -1 : a > b;
}
--
walter briscoe