man3/strverscmp.3

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.TH STRVERSCMP 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
strverscmp \- compare two version strings
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.B #include <string.h>
.PP
.BI "int strverscmp(const char *" s1 ", const char *" s2 );
.fi
.SH DESCRIPTION
Often one has files
.IR jan1 ", " jan2 ", ..., " jan9 ", " jan10 ", ..."
and it feels wrong when
.BR ls (1)
orders them
.IR jan1 ", " jan10 ", ..., " jan2 ", ..., " jan9 .
.\" classical solution: "rename jan jan0 jan?"
In order to rectify this, GNU introduced the
.I \-v
option to
.BR ls (1),
which is implemented using
.BR versionsort (3),
which again uses
.BR strverscmp ().
.PP
Thus, the task of
.BR strverscmp ()
is to compare two strings and find the "right" order, while
.BR strcmp (3)
finds only the lexicographic order.
This function does not use
the locale category
.BR LC_COLLATE ,
so is meant mostly for situations
where the strings are expected to be in ASCII.
.PP
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
.BR 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
.IR 000 ", " 00 ", " 01 ", " 010 ", " 09 ", " 0 ", " 1 ", " 9 ", " 10 .
.SH RETURN VALUE
The
.BR strverscmp ()
function returns an integer
less than, equal to, or greater than zero if
.I s1
is found, respectively, to be earlier than, equal to,
or later than
.IR s2 .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR strverscmp ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.\" FIXME: The marking is different from that in the glibc manual,
.\" which has:
.\"
.\"     strverscmp: MT-Safe locale
.\"
.\" glibc manual says strverscmp should have marking locale because it calls
.\" isdigit() multiple times and isdigit() uses locale variable.
.\" But isdigit() has two implementations. With different compiling conditions,
.\" we may call isdigit() in macro, then strverscmp() should not have locale
.\" problem.
.SH CONFORMING TO
This function is a GNU extension.
.SH EXAMPLES
The program below can be used to demonstrate the behavior of
.BR strverscmp ().
It uses
.BR strverscmp ()
to compare the two strings given as its command-line arguments.
An example of its use is the following:
.PP
.in +4n
.EX
$ \fB./a.out jan1 jan10\fP
jan1 < jan10
.EE
.in
.SS Program source
\&
.EX
#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>\en", argv[0]);
        exit(EXIT_FAILURE);
    }

    res = strverscmp(argv[1], argv[2]);

    printf("%s %s %s\en", argv[1],
            (res < 0) ? "<" : (res == 0) ? "==" : ">", argv[2]);

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR rename (1),
.BR strcasecmp (3),
.BR strcmp (3),
.BR strcoll (3)