strcmp(3) Library Functions Manual strcmp(3)
NAME
strcmp, strncmp - compare two strings
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <string.h>
int strcmp(const char *s1, const char *s2);
int strncmp(const char s1[.n], const char s2[.n], size_t n);
DESCRIPTION
The strcmp() function compares the two strings s1 and s2. The locale
is not taken into account (for a locale-aware comparison, see str-
coll(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.
RETURN VALUE
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.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌───────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────────────────┼───────────────┼─────────┤
│ strcmp(), strncmp() │ Thread safety │ MT-Safe │
└───────────────────────────────────────────┴───────────────┴─────────┘
VERSIONS
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 dif-
ference is 0.)
STANDARDS
C11, POSIX.1-2008.
HISTORY
POSIX.1-2001, C89, SVr4, 4.3BSD.
EXAMPLES
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 con-
taining 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
Program source
/* 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);
}
SEE ALSO
memcmp(3), strcasecmp(3), strcoll(3), string(3), strncasecmp(3),
strverscmp(3), wcscmp(3), wcsncmp(3), ascii(7)
Linux man-pages 6.7 2023-10-31 strcmp(3)
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