Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (4.4BSD-Lite2)
Apropos / Subsearch:
optional field

INET(3)                     BSD Programmer's Manual                    INET(3)

     inet_aton, inet_addr, inet_network, inet_ntoa, inet_makeaddr, inet_lnaof,
     inet_netof - Internet address manipulation routines

     #include <&lt;sys/socket.h>&gt;
     #include <&lt;netinet/in.h>&gt;
     #include <&lt;arpa/inet.h>&gt;

     inet_aton(char *cp, struct in_addr *pin);

     unsigned long
     inet_addr(char *cp);

     unsigned long
     inet_network(char *cp);

     char *
     inet_ntoa(struct in_addr in);

     struct in_addr
     inet_makeaddr(int net, int lna);

     unsigned long
     inet_lnaof(struct in_addr in);

     unsigned long
     inet_netof(struct in_addr in);

     The routines inet_aton(), inet_addr() and inet_network() interpret char-
     acter strings representing numbers expressed in the Internet standard `.'
     notation.  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 net-
     work numbers, respectively.  The routine inet_ntoa() takes an Internet
     address and returns an ASCII string representing the address in `.' nota-
     tion.  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 address-
     es, returning the network number and local network address part, respec-

     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.

     Values specified using the `.' notation take one of the following forms:


     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 ad-
     dress.  This makes the three part address format convenient for specify-
     ing 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, oc-
     tal, 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).

     The constant INADDR_NONE is returned by inet_addr() and inet_network()
     for malformed requests.

     gethostbyname(3),  getnetent(3),  hosts(5),  networks(5),

     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.

     Inet_addr should return a struct in_addr.

4.2 Berkeley Distribution        June 4, 1993                                2