strcmp, strncmp — compare two strings
#include <string.h>
int
strcmp( |
const char *s1, |
const char *s2); |
int
strncmp( |
const char *s1, |
| const char *s2, | |
size_t n); |
The strcmp() function
compares the two strings s1 and s2. The locale is not taken
into account (for a locale-aware comparison, see strcoll(3)). The comparison
is done using unsigned characters.
strcmp() returns an integer
indicating the result of the comparison, as follows:
0, if the s1
and s2 are
equal;
a negative value if s1 is less than
s2;
a positive value if s1 is greater than
s2.
The strncmp() function is
similar, except it compares only the first (at most)
n bytes of s1 and s2.
The strcmp() and
strncmp() functions return an
integer less than, equal to, or greater than zero if
s1 (or the first
n bytes thereof) is
found, respectively, to be less than, to match, or be greater
than s2.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
strcmp(), strncmp() |
Thread safety | MT-Safe |
POSIX.1 specifies only that:
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 unsigned char) that differ in the strings being compared.
In glibc, as in most other implementations, the return
value is the arithmetic result of subtracting the last
compared byte in s2
from the last compared byte in s1. (If the two characters are
equal, this difference is 0.)
The program below can be used to demonstrate the operation
of strcmp() (when given two
arguments) and strncmp() (when
given three arguments). First, some examples using
strcmp():
$ ./string_comp ABC ABC <str1> and <str2> are equal $ ./string_comp ABC AB # 'C' is ASCII 67; 'C' − '\0' = 67 <str1> is greater than <str2> (67) $ ./string_comp ABA ABZ # 'A' is ASCII 65; 'Z' is ASCII 90 <str1> is less than <str2> (−25) $ ./string_comp ABJ ABC <str1> is greater than <str2> (7) $ ./string_comp $'\201' A# 0201 − 0101 = 0100 (or 64 decimal) <str1> is greater than <str2> (64)
The last example uses bash(1)-specific syntax to produce a string containing an 8-bit ASCII code; the result demonstrates that the string comparison uses unsigned characters.
And then some examples using strncmp():
$ ./string_comp ABC AB 3 <str1> is greater than <str2> (67) $ ./string_comp ABC AB 2 <str1> and <str2> are equal in the first 2 bytes
/* 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>]\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\n", atoi(argv[3]));
printf("\n");
} else if (res < 0) {
printf("<str1> is less than <str2> (%d)\n", res);
} else {
printf("<str1> is greater than <str2> (%d)\n", res);
}
exit(EXIT_SUCCESS);
}
bcmp(3), memcmp(3), strcasecmp(3), strcoll(3), string(3), strncasecmp(3), strverscmp(3), wcscmp(3), wcsncmp(3), ascii(7)
This page is part of release 5.13 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright 1993 David Metcalfe (davidprism.demon.co.uk) and Copyright 2020 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END 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 (faithcs.unc.edu) Modified 2001-08-31, aeb |