inet_addr, inet_aton, inet_lnaof, inet_makeaddr, inet_netof,
inet_network, inet_ntoa, inet_ntop, inet_pton - Internet address manipulation
routines
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#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 *src, char *dst, size_t size);
int
inet_pton(int af, const char *src, void *dst);
The routines inet_aton(), inet_addr() and inet_network() interpret character
strings representing numbers expressed in the Internet
standard `.'
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 internal 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
parseable 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 successfully interpreted,
or 0 if the string was 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 routine
inet_ntoa() takes an Internet address and returns an ASCII
string representing
the address in `.' notation. The routine
inet_makeaddr() takes
an Internet network number and a local network address and
constructs an
Internet address from it. The routines inet_netof() and
inet_lnaof()
break apart Internet host addresses, returning 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 format integer values.
INTERNET ADDRESSES (IP VERSION 4) [Toc] [Back] Values specified using the `.' 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 (such as the
Intel 386,
486 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 rightmost 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 rightmost 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 `.' 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) [Toc] [Back] In order to support scoped IPv6 addresses, getaddrinfo(3)
and
getnameinfo(3) are 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 environment of IPv4 and IPv6 nodes is
x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal
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 representation). 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
The constant INADDR_NONE is returned by inet_addr() and
inet_network()
for malformed requests.
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.
The inet_ntop and inet_pton functions conform to the IETF
IPv6 BSD API
and address formatting specifications. 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.
The inet_addr, inet_network, inet_makeaddr, inet_lnaof and
inet_netof
functions appeared in 4.2BSD. The inet_aton and inet_ntoa
functions appeared
in 4.3BSD. The inet_pton and inet_ntop functions appeared in BIND
4.9.4.
The value INADDR_NONE (0xffffffff) is a valid broadcast address, but
inet_addr() cannot return that value without indicating
failure. Also,
inet_addr() should have been designed to return a struct
in_addr. The
newer inet_aton() function does not share these problems,
and almost all
existing code should be modified to use inet_aton() instead.
The problem of host byte ordering versus network byte ordering is confusing.
The string returned by inet_ntoa() resides in a static memory area.
OpenBSD 3.6 June 18, 1997
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