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 * restrict src
, char * restrict dst
, socklen_t size
)
int
inet_pton(
int af
, const char * restrict src
, void * restrict dst
)
),
inet_addr(
)
and
inet_network(
)
interpret character strings representing
numbers expressed in the Internet standard
"dotted quad
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 parsable 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 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
"dotted quad
notation.
The routine
inet_makeaddr()
takes an Internet network number and a local network address (both in
host order) and constructs an Internet address from it.
Note that to convert only a single value to a
struct
in_addr
form that value should be passed as the first parameter and
`0L'
should be given for the second parameter.
The routines
inet_netof()
and
inet_lnaof(
)
break apart Internet host addresses, returning the network number and
local network address part, respectively (both in host order).
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.
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 (e.g.
Intel i386, i486
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 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 "dotted quad 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 presentation format of an IPv6 address is given in RFC 2373:
There are three conventional forms for representing IPv6 addresses as text strings:
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).
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
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
INADDR_NONE
is returned by
inet_addr(
)
and
inet_network(
)
for malformed requests.
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
.