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

     inet_aton,	inet_addr, inet_network, inet_ntoa, inet_ntoa_r, inet_ntop,
     inet_pton,	inet_makeaddr, inet_lnaof, inet_netof -- Internet address ma-
     nipulation	routines

     Standard C	Library	(libc, -lc)

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/in.h>
     #include <arpa/inet.h>

     inet_aton(const char *cp, struct in_addr *pin);

     inet_addr(const char *cp);

     inet_network(const	char *cp);

     char *
     inet_ntoa(struct in_addr in);

     char *
     inet_ntoa_r(struct	in_addr	in, char *buf, socklen_t size);

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

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

     struct in_addr
     inet_makeaddr(in_addr_t net, in_addr_t lna);

     inet_lnaof(struct in_addr in);

     inet_netof(struct in_addr in);

     The routines inet_aton(), inet_addr() and inet_network() interpret	char-
     acter strings representing	numbers	expressed in the Internet standard `.'

     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 internal binary representation, in network
     byte order).  It returns 1	if the address was valid for the specified ad-
     dress family, or 0	if the address was not parseable in the	specified ad-
     dress 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

     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 successfully 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, re-

     The function inet_ntop() converts an address *src from network format
     (usually a	struct in_addr or some other binary form, in network byte or-
     der) to presentation format (suitable for external	display	purposes).
     The size argument specifies the size, in bytes, of	the buffer *dst.
     INET_ADDRSTRLEN and INET6_ADDRSTRLEN define the maximum size required to
     convert an	address	of the respective type.	 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.	 This function is presently valid for
     AF_INET and AF_INET6.

     The routine inet_ntoa() takes an Internet address and returns an ASCII
     string representing the address in	`.' notation.  The routine
     inet_ntoa_r() is the reentrant version of inet_ntoa().  The routine
     inet_makeaddr() takes an Internet network number and a local network ad-
     dress and constructs an Internet address from it.	The routines
     inet_netof() and inet_lnaof() break apart Internet	host addresses,	re-
     turning the network number	and local network address part,	respectively.

     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	byte order integer values.

     Values specified using the	`.' notation take one of the following forms:


     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	the VAX	the bytes referred to above appear as "d.c.b.a".  That is, VAX
     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 ad-
     dress.  This makes	the three part address format convenient for specify-
     ing Class B network addresses as "".

     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 specify-
     ing Class A network addresses as "".

     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 `.' 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).

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

     The inet_ntop() call fails	if:

     [ENOSPC]		size was not large enough to store the presentation
			form of	the address.

     [EAFNOSUPPORT]	*src was not an	AF_INET	or AF_INET6 family address.

     byteorder(3), getaddrinfo(3), gethostbyname(3), getnameinfo(3),
     getnetent(3), inet_net(3),	hosts(5), networks(5)

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

     The inet_ntop() and inet_pton() functions conform to X/Open Networking
     Services Issue 5.2	("XNS5.2").  Note that inet_pton() does	not accept 1-,
     2-, or 3-part dotted addresses; all four parts must be specified and are
     interpreted only as decimal values.  This is a narrower input set than
     that accepted by inet_aton().

     These functions appeared in 4.2BSD.

     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.

     The inet_addr() function should return a struct in_addr.

BSD				 June 14, 2007				   BSD


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