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


cc ... -lsocket

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

unsigned long inet_addr(cp) const char *cp;

unsigned long inet_network(cp) const char *cp;

int inet_aton(cp, val) const char *cp; struct in_addr *val;

char *inet_ntoa(in) struct in_addr in;

struct in_addr inet_makeaddr(net, lna) unsigned long net, lna;

unsigned long inet_lnaof(in) struct in_addr in;

unsigned long inet_netof(in) struct in_addr in;


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. inet_addr is implemented in terms of inet_aton. inet_aton allows for disambiguation between an address of all ones (such as a local broadcast address) and an error condition. inet_aton returns 1 if the address is valid, 0 otherwise.

The routine inet_ntoa takes an Internet address and returns an ASCII string representing the address in dot 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 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 dot 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.

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

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

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 ``dot'' 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).


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


The string returned by inet_ntoa resides in a static memory area which is overwritten by each call.

See also

gethostbyname(SLIB), getnetent(SLIB), hosts(SFF), inet(ADMP), networks(SFF)
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003