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Subject: Re: how is strnatcmp aka "Interpret numbers while sorting" supposed to sort?

Re: how is strnatcmp aka "Interpret numbers while sorting" supposed to sort?

From: codemonkey <codemonkey_at_interthingy.net>
Date: Thu, 19 Mar 2009 11:03:29 -0700

Are you guys aware that there's a quasi-standard regarding this in
the GNU libraries? See the following excerpt from Fedora "info ls"
and "man strverscmp".

~ray

PS: I've found that "ls -v" works well for sorting MP3s with track
numbering, etc. I don't know if it handles all of the cases described in
this thread though. Maybe GNU's implementation is worth borrowing for
rockbox?

------

$ info ls

(...excerpt...)

10.1.4 More details about version sort
--------------------------------------

The version sort takes into account the fact that file names frequently
include indices or version numbers. Standard sorting functions usually
do not produce the ordering that people expect because comparisons are
made on a character-by-character basis. The version sort addresses
this problem, and is especially useful when browsing directories that
contain many files with indices/version numbers in their names:

     $ ls -1 $ ls -1v
     foo.zml-1.gz foo.zml-1.gz
     foo.zml-100.gz foo.zml-2.gz
     foo.zml-12.gz foo.zml-6.gz
     foo.zml-13.gz foo.zml-12.gz
     foo.zml-2.gz foo.zml-13.gz
     foo.zml-25.gz foo.zml-25.gz
     foo.zml-6.gz foo.zml-100.gz

   Note also that numeric parts with leading zeros are considered as
fractional one:

     $ ls -1 $ ls -1v
     abc-1.007.tgz abc-1.007.tgz
     abc-1.012b.tgz abc-1.01a.tgz
     abc-1.01a.tgz abc-1.012b.tgz

   This functionality is implemented using the `strverscmp' function.

------

$ man strverscmp

STRVERSCMP(3) Linux Programmer’s Manual
STRVERSCMP(3)

NAME
       strverscmp - compare two version strings

SYNOPSIS
       #define _GNU_SOURCE
       #include <string.h>

       int strverscmp(const char *s1, const char *s2);

DESCRIPTION
       Often one has files jan1, jan2, ..., jan9, jan10, ... and it
feels
       wrong when ls(1) orders them jan1, jan10, ..., jan2, ..., jan9. In
       order to rectify this, GNU introduced the -v option to ls(1), which
is
       implemented using versionsort(3), which again uses strverscmp().

       Thus, the task of strverscmp() is to compare two strings and
find
       the "right" order, while strcmp(3) only finds the lexicographic
order.
       This function does not use the locale category LC_COLLATE, so is
meant
       mostly for situations where the strings are expected to be in
ASCII.

       What this function does is the following. If both strings are
equal,
       return 0. Otherwise find the position between two bytes with the
       property that before it both strings are equal, while directly after
it
       there is a difference. Find the largest consecutive digit strings
       containing (or starting at, or ending at) this position. If one or
both
       of these is empty, then return what strcmp(3) would have returned
       (numerical ordering of byte values). Otherwise, compare both digit
       strings numerically, where digit strings with one or more leading
zeroes
       are interpreted as if they have a decimal point in front (so that in
       particular digit strings with more leading zeroes come before digit
       strings with fewer leading zeroes). Thus, the ordering is 000,
00,
       01, 010, 09, 0, 1, 9, 10.

RETURN VALUE
       The strverscmp() function returns an integer less than, equal to, or
       greater than zero if s1 is found, respectively, to be earlier than,
       equal to, or later than s2.

CONFORMING TO
       This function is a GNU extension.

SEE ALSO
       rename(1), strcasecmp(3), strcmp(3), strcoll(3),
feature_test_macros(7)

GNU 2001-12-19
STRVERSCMP(3)
Received on 2009-03-19


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