Node:Networks Database,
Previous:Socket Options,
Up:Sockets
Networks Database
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
.
This data type is used to represent information about entries in the
networks database. It has the following members:
char *n_name
- This is the "official" name of the network.
char **n_aliases
- These are alternative names for the network, represented as a vector
of strings. A null pointer terminates the array.
int n_addrtype
- 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.
struct netent * getnetbyname (const char *name)
|
Function |
The getnetbyname function returns information about the network
named name. It returns a null pointer if there is no such
network.
|
struct netent * getnetbyaddr (unsigned long int net, int type)
|
Function |
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
network.
|
You can also scan the networks database using setnetent
,
getnetent
and endnetent
. Be careful when using these
functions because they are not reentrant.
void setnetent (int stayopen)
|
Function |
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.
|
struct netent * getnetent (void)
|
Function |
This function returns the next entry in the networks database. It
returns a null pointer if there are no more entries.
|
void endnetent (void)
|
Function |
This function closes the networks database.
|