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

NAME

     strverscmp - compare two version strings

SYNOPSIS

     #define _GNU_SOURCE         /* See feature_test_macros(7) */
     #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)  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 con-
     taining  (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.

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.

ATTRIBUTES

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).

     +-------------+---------------+---------+
     |Interface    | Attribute     | Value   |
     +-------------+---------------+---------+
     |strverscmp() | Thread safety | MT-Safe |
     +-------------+---------------+---------+

CONFORMING TO

     This function is a GNU extension.

EXAMPLE

     The  program  below  can be used to demonstrate the behavior of strver-
     scmp().  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 <string.h> #include <stdio.h> #include
     <stdlib.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); }