inet(3)

NAME

inet_aton, inet_addr, inet_network, inet_ntoa, inet_ntop,

inet_pton,
inet_makeaddr, inet_lnaof, inet_netof - Internet address ma

nipulation
routines

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int
inet_aton(const char *cp, struct in_addr *pin);
in_addr_t
inet_addr(const char *cp);
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);
struct in_addr
inet_makeaddr(in_addr_t net, in_addr_t lna);
in_addr_t
inet_lnaof(struct in_addr in);
in_addr_t
inet_netof(struct in_addr in);

DESCRIPTION

The routines inet_aton(), inet_addr() and inet_network() in

terpret character strings representing numbers expressed in the Internet

standard `.'
notation.

The inet_pton() function converts a presentation format ad

dress (that is,
printable form as held in a character string) to network

format (usually
a struct in_addr or some other internal binary representa

tion, in network
byte order). It returns 1 if the address was valid for the

specified
address family, or 0 if the address was not 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
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 *src from net

work format
(usually a struct in_addr or some other binary form, in net

work byte
order) to presentation format (suitable for external display

purposes).
The size argument specifies the size, in bytes, of the

buffer *dst. 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 re

turns an ASCII
string representing the address in `.' notation. The rou

tine
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 ad

dresses,
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 byte order integer values.

INTERNET ADDRESSES

Values specified using the `.' notation take one of the fol

lowing 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 Inter

net address.
Note that when an Internet address is viewed as a 32-bit in

teger 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 in

terpreted as a
16-bit quantity and placed in the right-most two bytes of

the network
address. This makes the three part address format conve

nient for specifying Class B network addresses as ``128.net.host''.

When a two part address is supplied, the last part is inter

preted 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 `.' 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 inet_aton() and inet_ntoa() functions are semi-deprecat

ed in favor of
the addr2ascii(3) family. However, since those functions

are not yet
widely implemented, portable programs cannot rely on their

presence and
will continue to use the inet(3) functions for some time.

DIAGNOSTICS

The constant INADDR_NONE is returned by inet_addr() and

inet_network()
for malformed requests.

ERRORS

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 fami

ly address.

SEE ALSO

addr2ascii(3), byteorder(3), gethostbyname(3), getnetent(3),

inet_net(3),
hosts(5), networks(5)

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

STANDARDS

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().

HISTORY

These functions appeared in 4.2BSD.

BUGS

The value INADDR_NONE (0xffffffff) is a valid broadcast ad

dress, 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 confus

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

Inet_addr should return a struct in_addr.

BSD June 14, 2004

BSD