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NetBSD 6.1.5 - man page for inet_ntop (netbsd section 3)

INET(3) 			   BSD Library Functions Manual 			  INET(3)

NAME
     inet_addr, inet_aton, inet_lnaof, inet_makeaddr, inet_netof, inet_network, inet_ntoa,
     inet_ntop, inet_pton, addr, ntoa, network -- Internet address manipulation routines

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <arpa/inet.h>

     in_addr_t
     inet_addr(const char *cp);

     int
     inet_aton(const char *cp, struct in_addr *addr);

     in_addr_t
     inet_lnaof(struct in_addr in);

     struct in_addr
     inet_makeaddr(in_addr_t net, in_addr_t lna);

     in_addr_t
     inet_netof(struct in_addr in);

     in_addr_t
     inet_network(const char *cp);

     char *
     inet_ntoa(struct in_addr in);

     const char *
     inet_ntop(int af, const void * restrict src, char * restrict dst, socklen_t size);

     int
     inet_pton(int af, const char * restrict src, void * restrict dst);

DESCRIPTION
     The routines inet_aton(), inet_addr() and inet_network() interpret character strings repre-
     senting numbers expressed in the Internet standard "dotted quad" notation.

     The inet_pton() function converts a presentation format address (that is, printable form as
     held in a character string) to network format (usually a struct in_addr or some other inter-
     nal binary representation, in network byte order).  It returns 1 if the address was valid
     for the specified address family, or 0 if the address wasn't parsable in the specified
     address family, or -1 if some system error occurred (in which case errno will have been
     set).  This function is presently valid for AF_INET and AF_INET6.

     The inet_aton() routine interprets the specified character string as an Internet address,
     placing the address into the structure provided.  It returns 1 if the string was success-
     fully interpreted, or 0 if the string is invalid.

     The inet_addr() and inet_network() functions return numbers suitable for use as Internet
     addresses and Internet network numbers, respectively.

     The function inet_ntop() converts an address from network format (usually a struct in_addr
     or some other binary form, in network byte order) to presentation format (suitable for
     external display purposes).  It returns NULL if a system error occurs (in which case, errno
     will have been set), or it returns a pointer to the destination string.  The size parameter
     is the size of the buf argument.

     The routine inet_ntoa() takes an Internet address and returns an ASCII string representing
     the address in "dotted quad" notation.

     The routine inet_makeaddr() takes an Internet network number and a local network address
     (both in host order) and constructs an Internet address from it.  Note that to convert only
     a single value to a struct in_addr form that value should be passed as the first parameter
     and '0L' should be given for the second parameter.

     The routines inet_netof() and inet_lnaof() break apart Internet host addresses, returning
     the network number and local network address part, respectively (both in host order).

     All Internet addresses are returned in network order (bytes ordered from left to right).
     All network numbers and local address parts are returned as machine format integer values.

INTERNET ADDRESSES (IP VERSION 4)
     Values specified using the "dotted quad" notation take one of the following forms:

	   a.b.c.d
	   a.b.c
	   a.b
	   a

     When four parts are specified, each is interpreted as a byte of data and assigned, from left
     to right, to the four bytes of an Internet address.  Note that when an Internet address is
     viewed as a 32-bit integer quantity on a system that uses little-endian byte order (e.g.
     Intel i386, i486 and Pentium processors) the bytes referred to above appear as ``d.c.b.a''.
     That is, little-endian bytes are ordered from right to left.

     When a three part address is specified, the last part is interpreted as a 16-bit quantity
     and placed in the right-most two bytes of the network address.  This makes the three part
     address format convenient for specifying Class B network addresses as ``128.net.host''.

     When a two part address is supplied, the last part is interpreted as a 24-bit quantity and
     placed in the right most three bytes of the network address.  This makes the two part
     address format convenient for specifying Class A network addresses as ``net.host''.

     When only one part is given, the value is stored directly in the network address without any
     byte rearrangement.

     All numbers supplied as ``parts'' in a "dotted quad" notation may be decimal, octal, or
     hexadecimal, as specified in the C language (i.e., a leading 0x or 0X implies hexadecimal;
     otherwise, a leading 0 implies octal; otherwise, the number is interpreted as decimal).

INTERNET ADDRESSES (IP VERSION 6)
     In order to support scoped IPv6 addresses, the use of getaddrinfo(3) and getnameinfo(3) is
     recommended rather than the functions presented here.

     The presentation format of an IPv6 address is given in RFC 2373:

     There are three conventional forms for representing IPv6 addresses as text strings:

     1.   The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hexadecimal values of the
	  eight 16-bit pieces of the address.  Examples:

		FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
		1080:0:0:0:8:800:200C:417A

	  Note that it is not necessary to write the leading zeros in an individual field, but
	  there must be at least one numeral in every field (except for the case described in 2).

     2.   Due to the method of allocating certain styles of IPv6 addresses, it will be common for
	  addresses to contain long strings of zero bits.  In order to make writing addresses
	  containing zero bits easier, a special syntax is available to compress the zeros.  The
	  use of ``::'' indicates multiple groups of 16-bits of zeros.	The ``::'' can only
	  appear once in an address.  The ``::'' can also be used to compress the leading and/or
	  trailing zeros in an address.

	  For example the following addresses:

		1080:0:0:0:8:800:200C:417A  a unicast address
		FF01:0:0:0:0:0:0:43	    a multicast address
		0:0:0:0:0:0:0:1 	    the loopback address
		0:0:0:0:0:0:0:0 	    the unspecified addresses

	  may be represented as:

		1080::8:800:200C:417A	    a unicast address
		FF01::43		    a multicast address
		::1			    the loopback address
		::			    the unspecified addresses

     3.   An alternative form that is sometimes more convenient when dealing with a mixed envi-
	  ronment of IPv4 and IPv6 nodes is x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadeci-
	  mal values of the six high-order 16-bit pieces of the address, and the 'd's are the
	  decimal values of the four low-order 8-bit pieces of the address (standard IPv4 repre-
	  sentation).  Examples:

		0:0:0:0:0:0:13.1.68.3
		0:0:0:0:0:FFFF:129.144.52.38

	  or in compressed form:

		::13.1.68.3
		::FFFF:129.144.52.38

DIAGNOSTICS
     The constant INADDR_NONE is returned by inet_addr() and inet_network() for malformed
     requests.

SEE ALSO
     byteorder(3), gethostbyname(3), getnetent(3), inet_net(3), hosts(5), networks(5)

     IP Version 6 Addressing Architecture, RFC 2373, July 1998.

     Basic Socket Interface Extensions for IPv6, RFC 3493, February 2003.

STANDARDS
     The inet_ntop and inet_pton functions conform to IEEE Std 1003.1-2001 (``POSIX.1'').  Note
     that inet_pton does not accept 1-, 2-, or 3-part  dotted addresses; all four parts must be
     specified.  This is a narrower input set than that accepted by inet_aton.

HISTORY
     The inet_addr, inet_network, inet_makeaddr, inet_lnaof and inet_netof functions appeared in
     4.2BSD.  They were changed to use in_addr_t in place of unsigned long in NetBSD 2.0.  The
     inet_aton and inet_ntoa functions appeared in 4.3BSD.  The inet_pton and inet_ntop functions
     appeared in BIND 4.9.4 and thence NetBSD 1.3; they were also in X/Open Networking Services
     Issue 5.2 (``XNS5.2'').

BUGS
     The value INADDR_NONE (0xffffffff) is a valid broadcast address, but inet_addr() cannot
     return that value without indicating failure.  The newer inet_aton() function does not share
     this problem.

     The problem of host byte ordering versus network byte ordering is confusing.

     The string returned by inet_ntoa() resides in a static memory area.

     inet_addr() should return a struct in_addr.

BSD					September 22, 2011				      BSD


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