centos man page for strcmp

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 correspond-
       ing 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()  func-
       tion  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
");
		  }
	      }
	      ...

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 Technol-
       ogy -- 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 original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								STRCMP(3P)