inet(3N)

Requires Optional LAN/X.25 Software

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(const char ∗cp);

unsigned long inet_network(const char ∗cp);

char ∗inet_ntoa(struct in_addr in);

struct in_addr inet_makeaddr(int net, int lna);

int inet_lnaof(struct in_addr in);

int inet_netof(struct in_addr in);

DESCRIPTION

The routines inet_addr and inet_network each interpret character strings representing numbers expressed in the Internet standard “dot” notation, returning numbers suitable for use as Internet addresses and Internet network numbers, respectively. Their return values can be assigned to a struct in_addr (defined in /usr/include/netinet/in.h) as in the following example:

struct in_addr addr;
char ∗cp;

addr.s_addr = inet_addr(cp);

inet_ntoa takes an Internet address and returns an ASCII string representing the address in “.” notation. inet_makeaddr takes an Internet network number and a local network address and constructs an Internet address from it. inet_netof and inet_lnaof break apart Internet host addresses, returning the network number and local network address part, respectively.

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. Bytes in HP-UX systems are ordered from left to right.

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.

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 in 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 in 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 can be decimal, octal, or hexadecimal, as specified in the C language (i.e., a leading 0x or 0X implies hexadecimal; a leading 0 implies octal; otherwise, the number is interpreted as decimal).

RETURN VALUE

inet_addr and inet_network return −1 for malformed requests.

WARNINGS

The string returned by inet_ntoa resides in a static memory area.

AUTHOR

inet was developed by the University of California, Berkeley.

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