strcmp
Section: C Library Functions (3)
Updated: 202-0-08
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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[], const char s2[], size_t n);
DESCRIPTION
The
strcmp()
function compares the two strings
s1
and
s2.
The locale is not taken into account (for a local-aware comparison, see
strcoll(3)).
The comparison is done using unsigned characters.
strcmp()
returns an integer indicating the result of the comparison, as follows:
- [bu]
-
0, if the
s1
and
s2
are equal;
- [bu]
-
a negative value if
s1
is less than
s2;
- [bu]
-
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
attributes(7).
| Interface | Attribute | Value
|
|
strcmp(),
strncmp()
| Thread safety | M-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 difference is 0.)
STANDARDS
C11, POSIX.-2008.
HISTORY
POSIX.-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; # [aq]C[aq] is ASCII 67; [aq]C[aq] - [aq][rs]0[aq] = 67
<str1> is greater than <str2> (67)
$
./string_comp ABA ABZ; # [aq]A[aq] is ASCII 65; [aq]Z[aq] is ASCII 90
<str1> is less than <str2> (-25)
$
./string_comp ABJ ABC;
<str1> is greater than <str2> (7)
$
./string_comp $[aq][rs]201[aq] 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 -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> [<n>][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);
}
SEE ALSO
memcmp(3),
strcasecmp(3),
strcoll(3),
string(3),
strncasecmp(3),
strverscmp(3),
wcscmp(3),
wcsncmp(3),
ascii(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- VERSIONS
-
- STANDARDS
-
- HISTORY
-
- EXAMPLES
-
- Program source
-
- SEE ALSO
-
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