It is possible
(but not required) to specify a default address for a remote datagram
socket.
This allows you to send messages without specifying the remote
address each time. In fact, if you use sendto
or sendmsg, an error occurs if
you enter any value other than 0 for the socket address after the
default address has been recorded. You can use send
or write
instead of sendto
or sendmsg once you have specified
the default address.
Use recv for receiving messages.
Although recvfrom can be used, it is
not necessary, because you already know that the message came from
the default remote socket. (Messages from sockets other than the
default socket are discarded without notice.) read(2)
can also be used, but does not allow
you to use the MSG_PEEK
flag.
Specify the default address with the connect
system call. connect
recognizes two special default addresses, INADDR_ANY and INADDR_BROADCAST.
Using INADDR_ANY connects your socket to the IP address of your
local host's primary LAN interface (for loopback connections). Using
INADDR_BROADCAST connects your socket to the subnet broadcast address
for your primary LAN interface; it allows you to send out broadcast
packets that interface without specifying the subnet broadcast address.
When a datagram socket descriptor is specified in a connect
call, connect associates the specified
socket with a particular remote socket address. connect
returns immediately because it only records the peer's socket address.
After connect records the default
address, any message sent from that socket is automatically addressed
to the peer process and only messages from that peer are delivered
to the socket.
connect may be called any
number of times to change the associated destination address.
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 | NOTE: This call does not behave the same as a connect
for stream sockets. There is no connection, just a default destination.
The remote host that you specify as the default may or may not use
connect to specify your local host
as its default remote host. The default remote host is not
notified if your local socket is destroyed. |
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connect and its parameters
are described in the following table.
- Include files:
#include<sys/types.h>
#include<netinet/in.h>
#include<sys/socket.h> |
- System call:
connect(s,addr,addrlen)
int s;
struct sockaddr*addr;
int addrlen; |
- Function result:
0 if connect is successful, -1 if failure
occurs.
When to Specify a Default Socket Address |
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The client or server process should specify a default socket
address after sockets are bound.
