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 (con-
       sult 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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    STRCMP(3P)