qsort_r()

[Douglas Bagnall]

On 24/03/18 14:15, Timur I. Bakeyev via samba-technical wrote:

> On unrelated note I want to remind everyone that at least for FreeBSD:
> 
>     The algorithms implemented by qsort(), qsort_r(), and heapsort() are _not_
>      stable, that is, if two members compare as equal, their order in the
>      sorted array is undefined.
> 
> We've been bitten by this at least once. So something to keep in mind...

This is actually also true with linux/glibc under memory pressure, where qsort()
et. al. abandon their surreptitious attempts at mergesort:

https://sourceware.org/git/?p=glibc.git;a=blob;f=stdlib/msort.c;h=266c2538c07e86d058359d47388fe21cbfdb525a;hb=refs/heads/master#l213

The documentation explicitly disclaims sort stability.

Douglas