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 manipu-
     lation 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 char-
     acter 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, respec-
     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 speci-
     fying 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 specify-
     ing 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; other-
     wise, the number is interpreted as decimal).

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 <netinet/in.h>
     #include <arpa/inet.h>

     These include files are necessary for all functions.

SEE ALSO
     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.

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 specified 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.

     The inet_addr() function should return a struct in_addr.

BSD                              June 14, 2007                             BSD