strverscmp - compare two version strings

#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.

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

Program source

#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)