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udp (Internet User Datagram Protocol)
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#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

socket(AF_INET, SOCK_DGRAM, 0);

UDP is a simple, unreliable datagram protocol which is used to support the SOCK_DGRAM abstraction for the Internet protocol family. UDP sockets are connectionless, and are normally used with the sendto and recvfrom calls, though the connect call may also be used to fix the destination for future packets (in which case the recv or read and send or write system calls may be used).

UDP address formats are identical to those used by TCP. 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 (i.e., a UDP port may not be 'connected' to a TCP port). In addition broadcast packets may be sent (assuming the underlying network supports this) by using a reserved 'broadcast address'; this address is network interface dependent.

Options at the IP transport level may be used with UDP; see IP).


A socket operation may fail with one of the following errors returned:

EISCONN when trying 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 is already connected
ENOTCONN when trying to send a datagram, but no destination address is specified, and the socket has not been connected
ENOBUFS when the system runs out of memory for an internal data structure
EADDRINUSE when an attempt is made to create a socket with a port which has already been allocated
EADDRNOTAVAIL when an attempt is made to create a socket with a network address for which no network interface exists

MIB Variables

The udp protocol implements a number of variables in the net.inet branch of the sysctl MIB.


The UDP protocol appeared in 4.2BSD.


Versions Link to
INtime 4.0 netlib.lib

See Also

getsockopt, recv, send, socket, blackhole, inet, IP