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>INET(3) System Library Functions Manual INET(3)
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NAME
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inet_addr, inet_aton, inet_lnaof, inet_makeaddr, inet_netof,
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inet_network, inet_ntoa, inet_ntop, inet_pton - Internet address manipu-
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lation routines
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SYNOPSIS
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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in_addr_t
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inet_addr(const char *cp);
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int
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inet_aton(const char *cp, struct in_addr *addr);
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in_addr_t
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inet_lnaof(struct in_addr in);
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struct in_addr
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inet_makeaddr(unsigned long net, unsigned long lna);
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in_addr_t
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inet_netof(struct in_addr in);
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in_addr_t
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inet_network(const char *cp);
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char *
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inet_ntoa(struct in_addr in);
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const char *
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inet_ntop(int af, const void *src, char *dst, size_t size);
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int
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inet_pton(int af, const char *src, void *dst);
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DESCRIPTION
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The routines inet_aton(), inet_addr() and inet_network() interpret char-
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acter strings representing numbers expressed in the Internet standard `.'
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notation. The inet_pton() function converts a presentation format
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address (that is, printable form as held in a character string) to net-
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work format (usually a struct in_addr or some other internal binary rep-
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resentation, in network byte order). It returns 1 if the address was
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valid for the specified address family, or 0 if the address wasn't
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parseable in the specified address family, or -1 if some system error
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occurred (in which case errno will have been set). This function is
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presently valid for AF_INET and AF_INET6. The inet_aton() routine inter-
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prets the specified character string as an Internet address, placing the
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address into the structure provided. It returns 1 if the string was suc-
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cessfully interpreted, or 0 if the string was invalid. The inet_addr()
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and inet_network() functions return numbers suitable for use as Internet
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addresses and Internet network numbers, respectively.
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The function inet_ntop() converts an address from network format (usually
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a struct in_addr or some other binary form, in network byte order) to
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presentation format (suitable for external display purposes). It returns
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NULL if a system error occurs (in which case, errno will have been set),
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or it returns a pointer to the destination string. The routine
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inet_ntoa() takes an Internet address and returns an ASCII string repre-
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senting the address in `.' notation. The routine inet_makeaddr() takes
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an Internet network number and a local network address and constructs an
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Internet address from it. The routines inet_netof() and inet_lnaof()
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break apart Internet host addresses, returning the network number and
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local network address part, respectively.
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All Internet addresses are returned in network order (bytes ordered from
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left to right). All network numbers and local address parts are returned
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as machine format integer values.
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INTERNET ADDRESSES (IP VERSION 4)
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Values specified using the `.' notation take one of the following forms:
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a.b.c.d
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a.b.c
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a.b
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a
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When four parts are specified, each is interpreted as a byte of data and
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assigned, from left to right, to the four bytes of an Internet address.
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Note that when an Internet address is viewed as a 32-bit integer quantity
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on a system that uses little-endian byte order (such as the Intel 386,
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486 and Pentium processors) the bytes referred to above appear as
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``d.c.b.a''. That is, little-endian bytes are ordered from right to
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left.
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When a three part address is specified, the last part is interpreted as a
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16-bit quantity and placed in the rightmost two bytes of the network
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address. This makes the three part address format convenient for speci-
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fying Class B network addresses as ``128.net.host''.
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When a two part address is supplied, the last part is interpreted as a
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24-bit quantity and placed in the rightmost three bytes of the network
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address. This makes the two part address format convenient for specify-
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ing Class A network addresses as ``net.host''.
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When only one part is given, the value is stored directly in the network
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address without any byte rearrangement.
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All numbers supplied as ``parts'' in a `.' notation may be decimal,
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octal, or hexadecimal, as specified in the C language (i.e., a leading 0x
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or 0X implies hexadecimal; otherwise, a leading 0 implies octal; other-
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wise, the number is interpreted as decimal).
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INTERNET ADDRESSES (IP VERSION 6)
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In order to support scoped IPv6 addresses, getaddrinfo(3) and
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getnameinfo(3) are recommended rather than the functions presented here.
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The presentation format of an IPv6 address is given in [RFC1884 2.2]:
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There are three conventional forms for representing IPv6 addresses as
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text strings:
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1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hex-
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adecimal values of the eight 16-bit pieces of the address. Exam-
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ples:
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FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
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1080:0:0:0:8:800:200C:417A
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Note that it is not necessary to write the leading zeros in an indi-
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vidual field, but there must be at least one numeral in every field
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(except for the case described in 2.).
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2. Due to the method of allocating certain styles of IPv6 addresses, it
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will be common for addresses to contain long strings of zero bits.
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In order to make writing addresses
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containing zero bits easier a special syntax is available to com-
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press the zeros. The use of ``::'' indicates multiple groups of 16
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bits of zeros. The ``::'' can only appear once in an address. The
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``::'' can also be used to compress the leading and/or trailing
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zeros in an address.
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For example the following addresses:
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1080:0:0:0:8:800:200C:417A a unicast address
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FF01:0:0:0:0:0:0:43 a multicast address
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0:0:0:0:0:0:0:1 the loopback address
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0:0:0:0:0:0:0:0 the unspecified addresses
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may be represented as:
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1080::8:800:200C:417A a unicast address
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FF01::43 a multicast address
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::1 the loopback address
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:: the unspecified addresses
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3. An alternative form that is sometimes more convenient when dealing
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with a mixed environment of IPv4 and IPv6 nodes is
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x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values of
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the six high-order 16-bit pieces of the address, and the 'd's are
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the decimal values of the four low-order 8-bit pieces of the address
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(standard IPv4 representation). Examples:
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0:0:0:0:0:0:13.1.68.3
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0:0:0:0:0:FFFF:129.144.52.38
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or in compressed form:
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::13.1.68.3
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::FFFF:129.144.52.38
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DIAGNOSTICS
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The constant INADDR_NONE is returned by inet_addr() and inet_network()
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for malformed requests.
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SEE ALSO
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byteorder(3), gethostbyname(3), getnetent(3), inet_net(3), hosts(5),
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networks(5)
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STANDARDS
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The inet_ntop and inet_pton functions conforms to the IETF IPv6 BSD API
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and address formatting specifications. Note that inet_pton does not
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accept 1-, 2-, or 3-part dotted addresses; all four parts must be speci-
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fied. This is a narrower input set than that accepted by inet_aton.
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HISTORY
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The inet_addr, inet_network, inet_makeaddr, inet_lnaof and inet_netof
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functions appeared in 4.2BSD. The inet_aton and inet_ntoa functions
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appeared in 4.3BSD. The inet_pton and inet_ntop functions appeared in
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BIND 4.9.4.
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BUGS
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| 280 |
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The value INADDR_NONE (0xffffffff) is a valid broadcast address, but
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inet_addr() cannot return that value without indicating failure. Also,
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inet_addr() should have been designed to return a struct in_addr. The
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newer inet_aton() function does not share these problems, and almost all
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existing code should be modified to use inet_aton() instead.
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The problem of host byte ordering versus network byte ordering is confus-
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ing.
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The string returned by inet_ntoa() resides in a static memory area.
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BSD June 18, 1997 BSD
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</PRE
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><A
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HREF="tcpip-library-reference.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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WIDTH="33%"
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>inet6_option_space</TD
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