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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 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 ALSO
       strncmp()
       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)