man3/strverscmp.3

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  26 .TH STRVERSCMP 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  27 .SH NAME
  28 strverscmp \- compare two version strings
  29 .SH SYNOPSIS
  30 .nf
  31 .BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
  32 .B #include <string.h>
  33 .PP
  34 .BI "int strverscmp(const char *" s1 ", const char *" s2 );
  35 .fi
  36 .SH DESCRIPTION
  37 Often one has files
  38 .IR jan1 ", " jan2 ", ..., " jan9 ", " jan10 ", ..."
  39 and it feels wrong when
  40 .BR ls (1)
  41 orders them
  42 .IR jan1 ", " jan10 ", ..., " jan2 ", ..., " jan9 .
  43 .\" classical solution: "rename jan jan0 jan?"
  44 In order to rectify this, GNU introduced the
  45 .I \-v
  46 option to
  47 .BR ls (1),
  48 which is implemented using
  49 .BR versionsort (3),
  50 which again uses
  51 .BR strverscmp ().
  52 .PP
  53 Thus, the task of
  54 .BR strverscmp ()
  55 is to compare two strings and find the "right" order, while
  56 .BR strcmp (3)
  57 finds only the lexicographic order.
  58 This function does not use
  59 the locale category
  60 .BR LC_COLLATE ,
  61 so is meant mostly for situations
  62 where the strings are expected to be in ASCII.
  63 .PP
  64 What this function does is the following.
  65 If both strings are equal, return 0.
  66 Otherwise, find the position
  67 between two bytes with the property that before it both strings are equal,
  68 while directly after it there is a difference.
  69 Find the largest consecutive digit strings containing (or starting at,
  70 or ending at) this position.
  71 If one or both of these is empty,
  72 then return what
  73 .BR strcmp (3)
  74 would have returned (numerical ordering of byte values).
  75 Otherwise, compare both digit strings numerically, where digit strings with
  76 one or more leading zeros are interpreted as if they have a decimal point
  77 in front (so that in particular digit strings with more leading zeros
  78 come before digit strings with fewer leading zeros).
  79 Thus, the ordering is
  80 .IR 000 ", " 00 ", " 01 ", " 010 ", " 09 ", " 0 ", " 1 ", " 9 ", " 10 .
  81 .SH RETURN VALUE
  82 The
  83 .BR strverscmp ()
  84 function returns an integer
  85 less than, equal to, or greater than zero if
  86 .I s1
  87 is found, respectively, to be earlier than, equal to,
  88 or later than
  89 .IR s2 .
  90 .SH ATTRIBUTES
  91 For an explanation of the terms used in this section, see
  92 .BR attributes (7).
  93 .TS
  94 allbox;
  95 lb lb lb
  96 l l l.
  97 Interface       Attribute       Value
  98 T{
  99 .BR strverscmp ()
 100 T}      Thread safety   MT-Safe
 101 .TE
 102 .\" FIXME: The marking is different from that in the glibc manual,
 103 .\" which has:
 104 .\"
 105 .\"     strverscmp: MT-Safe locale
 106 .\"
 107 .\" glibc manual says strverscmp should have marking locale because it calls
 108 .\" isdigit() multiple times and isdigit() uses locale variable.
 109 .\" But isdigit() has two implementations. With different compiling conditions,
 110 .\" we may call isdigit() in macro, then strverscmp() should not have locale
 111 .\" problem.
 112 .SH CONFORMING TO
 113 This function is a GNU extension.
 114 .SH EXAMPLE
 115 The program below can be used to demonstrate the behavior of
 116 .BR strverscmp ().
 117 It uses
 118 .BR strverscmp ()
 119 to compare the two strings given as its command-line arguments.
 120 An example of its use is the following:
 121 .PP
 122 .in +4n
 123 .EX
 124 $ \fB./a.out jan1 jan10\fP
 125 jan1 < jan10
 126 .EE
 127 .in
 128 .SS Program source
 129 \&
 130 .EX
 131 #define _GNU_SOURCE
 132 #include <string.h>
 133 #include <stdio.h>
 134 #include <stdlib.h>
 135
 136 int
 137 main(int argc, char *argv[])
 138 {
 139     int res;
 140
 141     if (argc != 3) {
 142         fprintf(stderr, "Usage: %s <string1> <string2>\en", argv[0]);
 143         exit(EXIT_FAILURE);
 144     }
 145
 146     res = strverscmp(argv[1], argv[2]);
 147
 148     printf("%s %s %s\en", argv[1],
 149             (res < 0) ? "<" : (res == 0) ? "==" : ">", argv[2]);
 150
 151     exit(EXIT_SUCCESS);
 152 }
 153 .EE
 154 .SH SEE ALSO
 155 .BR rename (1),
 156 .BR strcasecmp (3),
 157 .BR strcmp (3),
 158 .BR strcoll (3)