INET(3N)
NAME
inet_addr, inet_network, inet_ntoa, inet_makeaddr, inet_lnaof, inet_netof − Internet address manipulation routines
USAGE
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
struct in_addr inet_addr(cp)
char *cp;
int inet_network(cp)
char *cp;
char *inet_ntoa(in)
struct inet_addr in;
struct in_addr inet_makeaddr(net, lna)
int net, lna;
int inet_lnaof(in)
struct in_addr in;
int inet_netof(in)
struct in_addr in;
DESCRIPTION
The routines inet_addr and inet_network each interpret character strings that represent numbers expressed in the Internet standard “.” notation, and return 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 that represents 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, and return 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.
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 “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 zero implies octal. Numbers without a leading zero are interpreted as decimal).
NOTES
The string returned by inet_ntoa resides in a static memory area that is overwritten.
DIAGNOSTICS
Inet_addr and inet_network return the value −1 for erroneous requests.