| INET(3) | Library Functions Manual | INET(3) |
inet_addr,
inet_aton, inet_lnaof,
inet_makeaddr, inet_netof,
inet_network, inet_ntoa,
inet_ntop, inet_pton
— Internet address manipulation routines
Standard C Library (libc, -lc)
#include
<arpa/inet.h>
in_addr_t
inet_addr(const char *cp);
int
inet_aton(const char *cp,
struct in_addr *pin);
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);
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 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 network format (usually
a struct in_addr or some other binary form, in network
byte order) to presentation format (suitable for external display purposes).
The size argument specifies the size, in bytes, of the
buffer *dst. INET_ADDRSTRLEN
and INET6_ADDRSTRLEN define the maximum size
required to convert an address of the respective type. 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 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 byte order integer values.
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).
The constant INADDR_NONE is returned by
inet_addr() and
inet_network() for malformed requests.
The inet_ntop() call fails if:
EAFNOSUPPORT]AF_INET or
AF_INET6 family address.ENOSPC]#include
<sys/types.h> #include
<sys/socket.h> #include
<netinet/in.h> #include
<arpa/inet.h>
These include files are necessary for all functions.
byteorder(3), getaddrinfo(3), gethostbyname(3), getnameinfo(3), getnetent(3), inet_net(3), hosts(5), networks(5)
IP Version 6 Addressing Architecture, RFC, 2373, July 1998.
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. Any leading 0s will be stripped. This is a narrower input
set than that accepted by inet_aton().
These functions appeared in 4.2BSD.
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.
The inet_addr() function should return a
struct in_addr.
| June 14, 2007 | Mac OS X 12 |