Many systems come with a database that records a list of networks known
to the system developer. This is usually kept either in the file
`/etc/networks' or in an equivalent from a name server. This data
base is useful for routing programs such as route
, but it is not
useful for programs that simply communicate over the network. We
provide functions to access this database, which are declared in
`netdb.h'.
char *n_name
char **n_aliases
int n_addrtype
AF_INET
for Internet networks.
unsigned long int n_net
Use the getnetbyname
or getnetbyaddr
functions to search
the networks database for information about a specific network. The
information is returned in a statically-allocated structure; you must
copy the information if you need to save it.
getnetbyname
function returns information about the network
named name. It returns a null pointer if there is no such
network.
getnetbyaddr
function returns information about the network
of type type with number net. You should specify a value of
AF_INET
for the type argument for Internet networks.
getnetbyaddr
returns a null pointer if there is no such
network.
You can also scan the networks database using setnetent
,
getnetent
and endnetent
. Be careful when using these
functions because they are not reentrant.
If the stayopen argument is nonzero, this sets a flag so that
subsequent calls to getnetbyname
or getnetbyaddr
will
not close the database (as they usually would). This makes for more
efficiency if you call those functions several times, by avoiding
reopening the database for each call.
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