STRCMP(3)                  POSIX Programmer's Manual                 STRCMP(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       strcmp -- 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.1-2017
       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.

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 aa 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 ALSO
       strncmp()

       The Base Definitions volume of POSIX.1-2017, <string.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            STRCMP(3)
