|INET(3)||Library Functions Manual||INET(3)|
— Internet address manipulation routines
char *cp, struct in_addr
const char *
af, const void
*src, char *dst,
af, const char
inet_network() interpret character strings
representing numbers expressed in the Internet standard “dot”
inet_pton() function converts a
presentation format address (that is, printable form as held in a character
string) to network format (usually a
or some other internal binary representation, in network byte order). It
returns 1 if the address was valid for the specified address family; 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
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_network() functions return numbers suitable for
use as Internet addresses and Internet network numbers, respectively.
inet_ntop() converts an
address from network format (usually a
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
takes an Internet address and returns an ASCII string representing the
address in dot notation. The routine
takes an Internet network number and a local network address and constructs
an Internet address from it. The routines
inet_lnaof() break apart Internet host addresses,
returning the network number and local network address part,
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.
Values specified using dot 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
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
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 dot notation may be decimal, octal, or hexadecimal, as specified in the C language (i.e., a leading 0x or 0X implies hexadecimal; a leading 0 implies octal; otherwise, the number is interpreted as decimal).
The presentation format of an IPv6 address is given in RFC 2373:
There are three conventional forms for representing IPv6 addresses as text strings:
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.).
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
or in compressed form:
INADDR_NONE is returned by
inet_network() for malformed requests.
IP Version 6 Addressing Architecture, RFC 2373, July 1998.
Basic Socket Interface Extensions for IPv6, RFC 3493, February 2003.
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
functions appeared in 4.2BSD. The
functions appeared in 4.3BSD. The
functions appeared in BIND 4.9.4.
INADDR_NONE (0xffffffff) is a
valid broadcast address, but
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
The problem of host byte ordering versus network byte ordering is confusing.
The string returned by
in a static memory area.
|December 9, 2008||OpenBSD-5.1|