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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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strcmp(3) Library Functions Manual strcmp(3)
strcmp, strncmp - compare two strings
Standard C library (libc, -lc)
#include <string.h>
int strcmp(const char *s1, const char *s2);
int strncmp(const char s1[.n], const char s2[.n], 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.)
C11, POSIX.1-2008.
POSIX.1-2001, C89, SVr4, 4.3BSD.
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
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);
}
memcmp(3), strcasecmp(3), strcoll(3), string(3), strncasecmp(3),
strverscmp(3), wcscmp(3), wcsncmp(3), ascii(7)
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2024-06-26. If you discover any rendering problems in this HTML
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Linux man-pages 6.9.1 2024-06-15 strcmp(3)
Pages that refer to this page: bash(1), hsearch(3), memcmp(3), qsort(3), scandir(3), selinux_file_context_cmp(3), strcasecmp(3), strcoll(3), string(3), strverscmp(3), strxfrm(3), wcscmp(3), wcsncmp(3), signal-safety(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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