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Manual page for INET(3N)

inet inet_addr, inet_network, inet_makeaddr, inet_lnaof, inet_netof, inet_ntoa - Internet address manipulation


#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

unsigned long inet_addr(cp) char *cp;

inet_network(cp) char *cp;

struct in_addr inet_makeaddr(net, lna) int net, lna;

inet_lnaof(in) struct in_addr in;

inet_netof(in) struct in_addr in;

char * inet_ntoa(in) struct in_addr in;


The routines inet_addr() and inet_network() each interpret character strings representing numbers expressed in the Internet standard `.' notation, returning numbers suitable for use as Internet addresses and Internet network numbers, respectively. 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.

The routine inet_ntoa() returns a pointer to a string in the base 256 notation ``d.d.d.d'' described below.

All Internet address 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: when an Internet address is viewed as a 32-bit integer quantity on Sun386i systems, the bytes referred to above appear as d.c.b.a. That is, Sun386i 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 (that is, a leading 0x or 0X implies hexadecimal; otherwise, a leading 0 implies octal; otherwise, the number is interpreted as decimal).


gethostent.3n getnetent.3n hosts.5 networks.5


The value -1 is returned by inet_addr() and inet_network() for malformed requests.


The problem of host byte ordering versus network byte ordering is confusing. A simple way to specify Class C network addresses in a manner similar to that for Class B and Class A is needed.

The return value from inet_ntoa() points to static information which is overwritten in each call.

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Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).

Last modified 21/April/97