sendto()

PROTOTYPE

#include <sockets.h>

ssize_t sendto(int socket, void *buffer, size_t length, int flags, void *to, socklen_t tolen);

DESCRIPTION

sendto() is primarily used to send data over unconnected UDP sockets. TCP sockets and connected UDP sockets can only use sendto() if to is NULL, in which case sendto() behaves exactly like send(). Refer to the description of send() for more information.

For unconnected UDP sockets, to points to a structure (sockaddr_in or sockaddr_in6) containing the destination address. The IP address and port number must be in network byte order. tolen must be greater than or equal to the socket address size. If the socket has not been assigned a local port number, sendto() finds an unused port number and binds it to the socket.

If successful, sendto() returns the number of bytes sent. Otherwise, it sets errno and returns -1.

ERROR CODES

EACCES	to is a broadcast address and SO_BROADCAST is not set (UDP only).
EAFNOSUPPORT	Address family of the destination address doesn’t match the socket’s.
ECONNABORTED	Connection was aborted because of unacknowledged transmissions.
ECONNRESET	Connection was forcibly closed by remote host (received RST).
EDESTADDRREQ	Either the destination IP address or port number is zero.
EFAULT	buffer is NULL and length is not 0.
EHOSTUNREACH	Timed out after receiving a “host unreachable” ICMP message.
EINVAL	tolen is less than the socket address size.
EISCONN	to is not NULL and the socket is connected.
EMFILE	Socket not bound to local port number and no port is free (UDP only).
EMSGSIZE	length is larger than maximum datagram size (UDP only).
ENETDOWN	TargetTCP has not been initialized.
ENETUNREACH	No route exists to destination network (UDP only).
ENOBUFS	No buffer space available for datagram (UDP only).
ENOTCONN	The socket is not connected and to is NULL.
ENOTSOCK	socket is not a valid socket handle.
EOPNOTSUPP	MSG_OOB specified on UDP socket.
ESHUTDOWN	The socket has been shutdown for sending by shutdown().
ETIMEDOUT	Connection dropped because of no response from peer (TCP only).
EWOULDBLOCK	Socket is non-blocking and the send buffer is full (TCP only).

EXAMPLE

  int flag, rc, sock;
  struct sockaddr_in addr;

  /*-------------------------------------------------------------------*/
  /* Create a UDP socket.                                              */
  /*-------------------------------------------------------------------*/
  sock = socket(AF_INET, SOCK_DGRAM, 0);
  if (sock == -1) exit(errno);

  /*-------------------------------------------------------------------*/
  /* Set "send broadcast okay" flag.                                   */
  /*-------------------------------------------------------------------*/
  flag = TRUE;
  rc = setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &flag, sizeof(flag));
  if (rc < 0) exit(errno);

  /*-------------------------------------------------------------------*/
  /* Send "hello" to broadcast address.                                */
  /*-------------------------------------------------------------------*/
  bzero(&addr, sizeof(struct sockaddr_in));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(100);
  addr.sin_addr.s_addr = 0xFFFFFFFF;
  sendto(sock, "hello", 5, 0, &addr, sizeof(addr));