STRCMP(3P) POSIX Programmer's Manual STRCMP(3P)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.
NAMEstrcmp — compare two strings
SYNOPSIS
#include <string.h>
int strcmp(const char *s1, const char *s2);
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.1‐2008
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.
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.
ERRORS
No errors are defined.
The following sections are informative.
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");
}
}
...
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOstrncmp()
The Base Definitions volume of POSIX.1‐2008, <string.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 STRCMP(3P)
