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 correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
strcmp - compare two strings
SYNOPSIS
#include <string.h>
int strcmp(const char *s1, const char *s2);
DESCRIPTION
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() func-
tion 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
");
}
}
...
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
strncmp(), the Base Definitions volume of IEEE Std 1003.1-2001, <string.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
IEEE
/The Open Group 2003 STRCMP(3P)