man/man3/strcmp.3

'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2020 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 18:08:52 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2001-08-31, aeb
.\"
.TH strcmp 3 (date) "Linux man-pages (unreleased)"
.SH NAME
strcmp, strncmp \- compare two strings
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.P
.BI "int strcmp(const char *" s1 ", const char *" s2 );
.BI "int strncmp(const char " s1 [. n "], const char " s2 [. n "], size_t " n );
.fi
.SH DESCRIPTION
The
.BR strcmp ()
function compares the two strings
.I s1
and
.IR s2 .
The locale is not taken into account (for a locale-aware comparison, see
.BR strcoll (3)).
The comparison is done using unsigned characters.
.P
.BR strcmp ()
returns an integer indicating the result of the comparison, as follows:
.IP \[bu] 3
0, if the
.I s1
and
.I s2
are equal;
.IP \[bu]
a negative value if
.I s1
is less than
.IR s2 ;
.IP \[bu]
a positive value if
.I s1
is greater than
.IR s2 .
.P
The
.BR strncmp ()
function is similar, except it compares
only the first (at most)
.I n
bytes of
.I s1
and
.IR s2 .
.SH RETURN VALUE
The
.BR strcmp ()
and
.BR strncmp ()
functions return an integer
less than, equal to, or greater than zero if
.I s1
(or the first
.I n
bytes thereof) is found, respectively, to be less than, to
match, or be greater than
.IR s2 .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR strcmp (),
.BR strncmp ()
T}	Thread safety	MT-Safe
.TE
.SH VERSIONS
POSIX.1 specifies only that:
.RS
.P
The sign of a nonzero return value shall be determined by the sign
of the difference between the values of the first pair of bytes
(both interpreted as type
.IR "unsigned char" )
that differ in the strings being compared.
.RE
.P
In glibc, as in most other implementations,
the return value is the arithmetic result of subtracting
the last compared byte in
.I s2
from the last compared byte in
.IR s1 .
(If the two characters are equal, this difference is 0.)
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C89, SVr4, 4.3BSD.
.SH EXAMPLES
The program below can be used to demonstrate the operation of
.BR strcmp ()
(when given two arguments) and
.BR strncmp ()
(when given three arguments).
First, some examples using
.BR strcmp ():
.P
.in +4n
.EX
$ \fB./string_comp ABC ABC\fP
<str1> and <str2> are equal
$ \fB./string_comp ABC AB\fP      # \[aq]C\[aq] is ASCII 67; \[aq]C\[aq] \- \[aq]\[rs]0\[aq] = 67
<str1> is greater than <str2> (67)
$ \fB./string_comp ABA ABZ\fP     # \[aq]A\[aq] is ASCII 65; \[aq]Z\[aq] is ASCII 90
<str1> is less than <str2> (\-25)
$ \fB./string_comp ABJ ABC\fP
<str1> is greater than <str2> (7)
$ .\fB/string_comp $\[aq]\[rs]201\[aq] A\fP   # 0201 \- 0101 = 0100 (or 64 decimal)
<str1> is greater than <str2> (64)
.EE
.in
.P
The last example uses
.BR bash (1)-specific
syntax to produce a string containing an 8-bit ASCII code;
the result demonstrates that the string comparison uses unsigned
characters.
.P
And then some examples using
.BR strncmp ():
.P
.in +4n
.EX
$ \fB./string_comp ABC AB 3\fP
<str1> is greater than <str2> (67)
$ \fB./string_comp ABC AB 2\fP
<str1> and <str2> are equal in the first 2 bytes
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (string_comp.c)
.EX
/* string_comp.c
\&
   Licensed under GNU General Public License v2 or later.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
\&
int
main(int argc, char *argv[])
{
    int res;
\&
    if (argc < 3) {
        fprintf(stderr, "Usage: %s <str1> <str2> [<len>]\[rs]n", argv[0]);
        exit(EXIT_FAILURE);
    }
\&
    if (argc == 3)
        res = strcmp(argv[1], argv[2]);
    else
        res = strncmp(argv[1], argv[2], atoi(argv[3]));
\&
    if (res == 0) {
        printf("<str1> and <str2> are equal");
        if (argc > 3)
            printf(" in the first %d bytes\[rs]n", atoi(argv[3]));
        printf("\[rs]n");
    } else if (res < 0) {
        printf("<str1> is less than <str2> (%d)\[rs]n", res);
    } else {
        printf("<str1> is greater than <str2> (%d)\[rs]n", res);
    }
\&
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR memcmp (3),
.BR strcasecmp (3),
.BR strcoll (3),
.BR string (3),
.BR strncasecmp (3),
.BR strverscmp (3),
.BR wcscmp (3),
.BR wcsncmp (3),
.BR ascii (7)