[musl] Re: Different results with regex.h between Musl and Libc

[Valery Ushakov <uwe@stderr.spb.ru>]

On Mon, Jun 10, 2024 at 05:38:36 +0000, Nigel Kukard wrote:

> Musl output (Alpine 3.20), musl-1.2.5-r1...
> 
> The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> Match 0: 37
> Match 1:
> Match 2: 37
> 
> Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...
> 
> The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> Match 0: 37
> Match 1: 37
> Match 2:

I'm not sure what POSIX requires here.  The closest I can find after
skimming through "9. Regular Expressions" is 9.4.6 that ends with:

  An ERE matching a single character repeated by an '*', '?', or an
  interval expression shall not match a null expression unless this is
  the only match for the repetition or it is necessary to satisfy the
  exact or minimum number of occurrences for the interval expression.

    https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04_06

I'm not sure what to read into the absense of the usual "or an ERE
enclosed in parentheses" chorus here.


> printf("Match %d: %.*s\n", i, matches[i].rm_eo - matches[i].rm_so, input + matches[i].rm_so);

Nit-pick: regoff_t may be wider than int (expected by '*').  E.g. your
test program prints nothing for all those %.* on NetBSD/macppc (with
the appropriate cast it prints 37/37/<empty>), as regoff_t is 64-bit
(very old posix required regoff_t to be at least as wide as off_t).
It will probably crash on a little-endian 32-bit NetBSD system, b/c
the zero MSW of a 64-bit regoff_t will be interpreted as the argument
for %s.


-uwe