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Linux 2.6 - man page for strcmp (linux section 3posix)

STRCMP(P)			    POSIX Programmer's Manual				STRCMP(P)

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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					STRCMP(P)


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