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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.
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() 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  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 Technology
       -- 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)