INET(3)

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

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

unsigned long inet_addr(cp)
char *cp;

unsigned long inet_network(cp)
char *cp;

char *inet_ntoa(in)
struct in_addr in;

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

unsigned long inet_lnaof(in)
struct in_addr in;

unsigned long inet_netof(in)
struct in_addr in;

DESCRIPTION
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_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, respectively.

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.

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 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; otherwise, the number is interpreted as decimal).

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

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

BUGS
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 string returned by inet_ntoa resides in a static memory area.
Inet_addr should return a struct in_addr.