strverscmp — compare two version strings
#define _GNU_SOURCE #include <string.h>
int
strverscmp( |
const char * | s1, |
const char * | s2) ; |
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
.
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
.