STRCMP(3) Linux Programmer's Manual STRCMP(3)
NAME
 strcmp, strncmp - compare two strings
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 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:
 o 0, if the s1 and s2 are equal;
 o a negative value if s1 is less than s2;
 o 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 at-
 tributes(7).
 +--------------------+---------------+---------+
 |Interface | Attribute | Value |
 +--------------------+---------------+---------+
 |strcmp(), strncmp() | Thread safety | MT-Safe |
 +--------------------+---------------+---------+
CONFORMING TO
 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
NOTES
 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.)
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' - ' ' = 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円' A # 0201 -ひく 0101 =わ 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
 bcmp(3), memcmp(3), strcasecmp(3), strcoll(3), string(3), strn-
 casecmp(3), strverscmp(3), wcscmp(3), wcsncmp(3), ascii(7)
COLOPHON
 This page is part of release 5.10 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/.
 2020年04月11日 STRCMP(3)