сравнить две строки (compare two strings)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
strcmp — compare two strings
Синопсис (Synopsis)
#include <string.h>
int strcmp(const char *s1, const char *s2);
Описание (Description)
The functionality described on this reference page is aligned
with the ISO C standard. Any conflict between the requirements
described here and the ISO C standard is unintentional. This
volume of POSIX.1‐2017 defers to the ISO C standard.
The strcmp() function shall compare the string pointed to by s1
to the string pointed to by s2.
The sign of a non-zero 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.
Возвращаемое значение (Return value)
Upon completion, strcmp() shall return an integer greater than,
equal to, or less than 0, if the string pointed to by s1 is
greater than, equal to, or less than the string pointed to by s2,
respectively.
Ошибки (Error)
No errors are defined.
The following sections are informative.
Примеры (Examples)
Checking a Password Entry
The following example compares the information read from standard
input to the value of the name of the user entry. If the strcmp()
function returns 0 (indicating a match), a further check will be
made to see if the user entered the proper old password. The
crypt() function shall encrypt the old password entered by the
user, using the value of the encrypted password in the passwd
structure as the salt. If this value matches the value of the
encrypted passwd in the structure, the entered password oldpasswd
is the correct user's password. Finally, the program encrypts the
new password so that it can store the information in the passwd
structure.
#include <string.h>
#include <unistd.h>
#include <stdio.h>
...
int valid_change;
struct passwd *p;
char user[100];
char oldpasswd[100];
char newpasswd[100];
char savepasswd[100];
...
if (strcmp(p->pw_name, user) == 0) {
if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {
strcpy(savepasswd, crypt(newpasswd, user));
p->pw_passwd = savepasswd;
valid_change = 1;
}
else {
fprintf(stderr, "Old password is not valid\n");
}
}
...
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
strncmp(3p)
The Base Definitions volume of POSIX.1‐2017, string.h(0p)
