This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       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(3POSIX)

       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 unsignedchar) that  differ  in  the  strings  being
       compared.

       No errors are defined.

       Thefollowingsectionsareinformative.

CheckingaPasswordEntry
       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");
               }
           }
           ...

       None.

       strcmp — compare two strings

       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.

       None.

       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.

strncmp()

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

       #include <string.h>

       int strcmp(const char *s1, const char *s2);