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SYNOPSIS
cc ... -lsocket
#include <netdb.h>
struct netent *
getnetent();
struct netent *
getnetbyname(char name);
struct netent *
getnetbyaddr(unsigned long net, int type);
void
setnetent(int stayopen);
void
endnetent();
DESCRIPTION
The getnetent(), getnetbyname(), and getnetbyaddr() subroutines each re-
turn a pointer to an object with the following structure containing the
broken-out fields of a line in the networks database.
struct netent {
char *n_name; /* official name of net */
char **n_aliases; /* alias list */
int n_addrtype; /* net number type */
long n_net; /* net number */
};
The members of this structure are:
n_name The official name of the network.
n_aliases A zero-terminated list of alternate names for the network.
n_addrtype The type of the network number returned: AF_INET.
n_net The network number. Network numbers are returned in machine
byte order.
If the stayopen flag on a setnetent() subroutine is NULL, the networks
database is opened. Otherwise, the setnetent() has the effect of rewind-
ing the networks database. The endnetent() subroutine may be called to
close the networks database when processing is complete.
The getnetent() subroutine simply reads the next line while
getnetbyname() and getnetbyaddr() search until a matching name or net
number is found (or until EOF is encountered). The type must be AF_INET.
The getnetent() subroutine keeps a pointer in the database, allowing suc-
cessive calls to be used to search the entire file.
Before a while loop using getnetent(), a call to setnetent() must be made
in order to perform initialization; a call to endnetent() must be used
after the loop. Both getnetbyname() and getnetbyaddr() make calls to
setnetent() and endnetent().
FILES
/etc/networks
DIAGNOSTICS
Null pointer (0) returned on EOF or error.
SEE ALSO
networks(SFF), RFC 1101.
HISTORY
The getnetent(), getnetbyaddr(), getnetbyname(), setnetent(), and
endnetent() functions appeared in 4.2BSD.
BUGS
The data space used by these functions is static; if future use requires
the data, it should be copied before any subsequent calls to these func-
tions overwrite it. Only Internet network numbers are currently under-
stood. Expecting network numbers to fit in no more than 32 bits is prob-
ably naive.
4th Berkeley Distribution May 20, 1996