udp.4p

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)udp.4p	8.1	9/11/90
.TH udp 4p
.SH Name
udp \- Internet User Datagram Protocol
.SH Syntax
.B #include <sys/socket.h>
.br
.B #include <netinet/in.h>
.PP
.B s = socket(AF_INET, SOCK_DGRAM, 0);
.SH Description
.NXR "UDP"
.NXS "User Datagram Protocol" "UDP"
UDP is a simple, unreliable datagram protocol that is used
to support the SOCK_DGRAM abstraction for the Internet
protocol family.  UDP sockets are connectionless and are
normally used with the
.PN sendto 
and
.PN recvfrom 
calls, though the
.MS connect 2
call can also be used to fix the destination for future
packets (in which case the 
.MS recv 2
or
.MS read 2
and 
.MS send 2
or
.MS write 2
system calls may be used).
.PP
UDP address formats are identical to those used by
TCP. 
.NXR "UDP" "TCP and"
In particular, UDP provides a port identifier in addition
to the normal Internet address format.  Note that the UDP port
space is separate from the TCP port space (for example,  a UDP port
may not be ``connected'' to a TCP port).  In addition broadcast
packets can be sent (assuming the underlying network supports
this) by using a reserved ``broadcast address''; this address
is network interface dependent.  The SO_BROADCAST option must be
set on the socket for broadcasting to succeed.
.SH Diagnostics
A socket operation may fail with one of the following errors returned:
.TP 15
[EISCONN]
Try to establish a connection on a socket which
already has one, or when trying to send a datagram with the destination
address specified and the socket already connected.
.TP 15
[ENOTCONN]
Try to send a datagram, but
no destination address is specified, and the socket has not been
connected.
.TP 15
[ENOBUFS]
The system runs out of memory for
an internal data structure.
.TP 15
[EADDRINUSE]
An attempt
is made to create a socket with a port that has already been
allocated.
.TP 15
[EADDRNOTAVAIL]
An attempt is made to create a 
socket with a network address for which no network interface
exists.
.SH See Also
getsockopt(2), send(2), socket(2) recv(2), intro(4n), inet(4f)