NAME
inet_aton,
inet_addr, inet_network,
inet_ntoa, inet_makeaddr,
inet_lnaof, inet_netof
— Internet address manipulation
routines
SYNOPSIS
#include
<sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int
inet_aton(char
*cp, struct in_addr
*pin);
unsigned long
inet_addr(char
*cp);
unsigned long
inet_network(char
*cp);
char *
inet_ntoa(struct
in_addr in);
struct in_addr
inet_makeaddr(int
net, int lna);
unsigned long
inet_lnaof(struct
in_addr in);
unsigned long
inet_netof(struct
in_addr in);
DESCRIPTION
The routinesinet_aton(),
inet_addr()
and
inet_network()
interpret character strings representing numbers expressed in the Internet
standard ‘.’ notation. 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
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
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 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 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
‘.’ 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).
DIAGNOSTICS
The constant INADDR_NONE is returned by
inet_addr() and
inet_network() for malformed requests.
SEE ALSO
HISTORY
These functions appeared in 4.2BSD.
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.