INET(3) BSD Library Functions Manual INET(3)
NAME
inet_addr, inet_aton, inet_lnaof, inet_makeaddr, inet_netof, inet_network, inet_ntoa, inet_ntop,
inet_pton -- Internet address manipulation routines
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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);
DESCRIPTION
The routines inet_aton(), inet_addr(), and inet_network() interpret character strings representing num-bers numbers
bers 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 representa-tion, representation,
tion, in network byte order). It returns 1 if the address was valid for the specified address family,
or 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 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 pur-poses). purposes).
poses). The size argument specifies the size, in bytes, of the buffer *dst. It returns NULL if a sys-tem system
tem 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, respec-tively. respectively.
tively.
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 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 re-arrangement. rearrangement.
arrangement.
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-deprecated 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:
[EAFNOSUPPORT] *src was not an AF_INET or AF_INET6 family address.
[ENOSPC] size was not large enough to store the presentation form of the address.
LEGACY SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/netinet/in.h>
#include <sys/arpa/inet.h>
These include files are necessary for all functions.
SEE ALSO
addr2ascii(3), byteorder(3), gethostbyname(3), getnetent(3), inet_net(3), compat(5), 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 speci-fied specified
fied 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 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.
BSD June 14, 2004 BSD
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