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