man3/strverscmp.3

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  26 .TH STRVERSCMP 3  2016-10-08 "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 .br
  33 .B #include <string.h>
  34 .sp
  35 .BI "int strverscmp(const char *" s1 ", const char *" s2 );
  36 .fi
  37 .SH DESCRIPTION
  38 Often one has files
  39 .IR jan1 ", " jan2 ", ..., " jan9 ", " jan10 ", ..."
  40 and it feels wrong when
  41 .BR ls (1)
  42 orders them
  43 .IR jan1 ", " jan10 ", ..., " jan2 ", ..., " jan9 .
  44 .\" classical solution: "rename jan jan0 jan?"
  45 In order to rectify this, GNU introduced the
  46 .I \-v
  47 option to
  48 .BR ls (1),
  49 which is implemented using
  50 .BR versionsort (3),
  51 which again uses
  52 .BR strverscmp ().
  53
  54 Thus, the task of
  55 .BR strverscmp ()
  56 is to compare two strings and find the "right" order, while
  57 .BR strcmp (3)
  58 finds only the lexicographic order.
  59 This function does not use
  60 the locale category
  61 .BR LC_COLLATE ,
  62 so is meant mostly for situations
  63 where the strings are expected to be in ASCII.
  64
  65 What this function does is the following.
  66 If both strings are equal, return 0.
  67 Otherwise, find the position
  68 between two bytes with the property that before it both strings are equal,
  69 while directly after it there is a difference.
  70 Find the largest consecutive digit strings containing (or starting at,
  71 or ending at) this position.
  72 If one or both of these is empty,
  73 then return what
  74 .BR strcmp (3)
  75 would have returned (numerical ordering of byte values).
  76 Otherwise, compare both digit strings numerically, where digit strings with
  77 one or more leading zeros are interpreted as if they have a decimal point
  78 in front (so that in particular digit strings with more leading zeros
  79 come before digit strings with fewer leading zeros).
  80 Thus, the ordering is
  81 .IR 000 ", " 00 ", " 01 ", " 010 ", " 09 ", " 0 ", " 1 ", " 9 ", " 10 .
  82 .SH RETURN VALUE
  83 The
  84 .BR strverscmp ()
  85 function returns an integer
  86 less than, equal to, or greater than zero if
  87 .I s1
  88 is found, respectively, to be earlier than, equal to,
  89 or later than
  90 .IR s2 .
  91 .SH ATTRIBUTES
  92 For an explanation of the terms used in this section, see
  93 .BR attributes (7).
  94 .TS
  95 allbox;
  96 lb lb lb
  97 l l l.
  98 Interface       Attribute       Value
  99 T{
 100 .BR strverscmp ()
 101 T}      Thread safety   MT-Safe
 102 .TE
 103 .\" FIXME: The marking is different from that in the glibc manual,
 104 .\" which has:
 105 .\"
 106 .\"     strverscmp: MT-Safe locale
 107 .\"
 108 .\" glibc manual says strverscmp should have marking locale because it calls
 109 .\" isdigit() multiple times and isdigit() uses locale variable.
 110 .\" But isdigit() has two implementations. With different compiling conditions,
 111 .\" we may call isdigit() in macro, then strverscmp() should not have locale
 112 .\" problem.
 113 .SH CONFORMING TO
 114 This function is a GNU extension.
 115 .SH EXAMPLE
 116 The program below can be used to demonstrate the behavior of
 117 .BR strverscmp ().
 118 It uses
 119 .BR strverscmp ()
 120 to compare the two strings given as its command-line arguments.
 121 An example of its use is the following:
 122
 123 .in
 124 .in +4n
 125 .nf
 126 $ i\fB./a.out jan1 jan10\fP
 127 jan1 < jan10
 128 .fi
 129 .in
 130 .SS Program source
 131 \&
 132 .nf
 133 #define _GNU_SOURCE
 134 #include <string.h>
 135 #include <stdio.h>
 136 #include <stdlib.h>
 137
 138 int
 139 main(int argc, char *argv[])
 140 {
 141     int res;
 142
 143     if (argc != 3) {
 144         fprintf(stderr, "Usage: %s <string1> <string2>\\n", argv[0]);
 145         exit(EXIT_FAILURE);
 146     }
 147
 148     res = strverscmp(argv[1], argv[2]);
 149
 150     printf("%s %s %s\\n", argv[1],
 151             (res == \-1) ? "<" : (res == 0) ? "==" : ">", argv[2]);
 152
 153     exit(EXIT_SUCCESS);
 154 }
 155 .fi
 156 .SH SEE ALSO
 157 .BR rename (1),
 158 .BR strcasecmp (3),
 159 .BR strcmp (3),
 160 .BR strcoll (3)