In https://nullprogram.com/blog/2023/02/11/ you write:

> qsort is fine, though quality varies. [...] Similar story for bsearch.

I disagree! The big annoyance with these functions is that the callback
function doesn't take a user-provided context parameter, so that you
can't implement a sorting or searching criterion that varies over time.

  void qsort_as_it_should_be(void *array, size_t nmem, size_t size,
                             int (*cmp)(void *a, void *b, void *ctx),
                             void *ctx_to_pass_to_cmp);

An example might be if you've precomputed some auxiliary data that
doesn't fit in the main array, in order to use it as the sorting
criterion, and then you'll throw it away again afterwards.

Cheers,
Simon

-- 
for k in [pow(x,37,0x1a1298d262b49c895d47f) for x in [0x50deb914257022de7fff,
0x213558f2215127d5a2d1, 0x90c99e86d08b91218630, 0x109f3d0cfbf640c0beee7,
0xc83e01379a5fbec5fdd1, 0x19d3d70a8d567e388600e, 0x534e2f6e8a4a33155123]]:
 print("".join([chr(32+3*((k>>x)&1))for x in range(79)])) # <anakin@pobox.com>

> callback function doesn't take a user-provided context parameter

You're completely right, Simon. I've written on that issue in the past:

C Closures as a Library
https://nullprogram.com/blog/2017/01/08/

But I had forgotten about it here. So perhaps I should rank it lower than 
"fine." Though note that I hadn't described it as "good" or "great"!

On Sun, Feb 12, 2023 at 03:42:35PM +0000, Simon Tatham wrote:
> The big annoyance with these functions is that the callback function
> doesn't take a user-provided context parameter

There does exist qsort_s, but it's Annex K:
https://en.cppreference.com/w/c/algorithm/qsort

There also exists qsort_r, but it's a GNU extension (and FreeBSD's
qsort_r signature is incompatible with GNU's).

The good news is that qsort_r (the GNU version) is accepted into the
posix draft: https://www.austingroupbugs.net/view.php?id=900
Looks like the FreeBSD guys are going to deal with it via symbol
versioning. So perhaps it's not too long until it lands in the ISO C
standard as well.

- NRK