strverscmp - compare two version strings
Standard C library (
libc,
-lc)
#define _GNU_SOURCE /* See feature_test_macros(7) */
#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) finds only 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 zeros are interpreted as if they have a decimal point in
front (so that in particular digit strings with more leading zeros come before
digit strings with fewer leading zeros). 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.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
strverscmp () |
Thread safety |
MT-Safe |
This function is a GNU extension.
The program below can be used to demonstrate the behavior of
strverscmp(). It uses
strverscmp() to compare the two strings
given as its command-line arguments. An example of its use is the following:
$ ./a.out jan1 jan10
jan1 < jan10
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main(int argc, char *argv[])
{
int res;
if (argc != 3) {
fprintf(stderr, "Usage: %s <string1> <string2>\n", argv[0]);
exit(EXIT_FAILURE);
}
res = strverscmp(argv[1], argv[2]);
printf("%s %s %s\n", argv[1],
(res < 0) ? "<" : (res == 0) ? "==" : ">", argv[2]);
exit(EXIT_SUCCESS);
}
rename(1),
strcasecmp(3),
strcmp(3),
strcoll(3)