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
— Data Type: struct netent
This data type is used to represent information about entries in the
networks database. It has the following members:
This is the “official” name of the network.
These are alternative names for the network, represented as a vector
of strings. A null pointer terminates the array.
This is the type of the network number; this is always equal to
AF_INET for Internet networks.
unsigned long int n_net
This is the network number. Network numbers are returned in host
byte order; see Byte Order.
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.
The getnetbyname function returns information about the network
named name. It returns a null pointer if there is no such
— Function: struct netent * getnetbyaddr (unsigned long int net, int type)
The 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
You can also scan the networks database using setnetent,
getnetent and endnetent. Be careful when using these
functions because they are not reentrant.
— Function: void setnetent (int stayopen)
This function opens and rewinds the networks database.
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.
— Function: struct netent * getnetent (void)
This function returns the next entry in the networks database. It
returns a null pointer if there are no more entries.
— Function: void endnetent (void)
This function closes the networks database.
Published under the terms of the GNU General Public License