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@(#)send.2 6.5 (Berkeley) 02/14/89

C 5 send, sendto, sendmsg - send a message from a socket

#include <sys/types.h>
#include <sys/socket.h>

cc = send(s, msg, len, flags)
int cc, s;
char *msg;
int len, flags;

cc = sendto(s, msg, len, flags, to, tolen)
int cc, s;
char *msg;
int len, flags;
struct sockaddr *to;
int tolen;

cc = sendmsg(s, msg, flags)
int cc, s;
struct msghdr *msg;
int flags;

Send , sendto , and sendmsg are used to transmit a message to another socket. Send may be used only when the socket is in a connected state, while sendto and sendmsg may be used at any time.

The address of the target is given by to with tolen specifying its size. The length of the message is given by len . If the message is too long to pass atomically through the underlying protocol, then the error EMSGSIZE is returned, and the message is not transmitted.

No indication of failure to deliver is implicit in a send . Return values of -1 indicate some locally detected errors.

If no messages space is available at the socket to hold the message to be transmitted, then send normally blocks, unless the socket has been placed in non-blocking I/O mode. The select (2) call may be used to determine when it is possible to send more data.

The flags parameter may include one or more of the following:

#define MSG_OOB 0x1 /* process out-of-band data */
#define MSG_DONTROUTE 0x4 /* bypass routing, use direct interface */

The flag MSG_OOB is used to send \*(lqout-of-band\*(rq data on sockets that support this notion (e.g. SOCK_STREAM); the underlying protocol must also support \*(lqout-of-band\*(rq data. MSG_DONTROUTE is usually used only by diagnostic or routing programs.

See recv (2) for a description of the msghdr structure.

The call returns the number of characters sent, or -1 if an error occurred.

20 [EBADF] An invalid descriptor was specified.

20 [ENOTSOCK] The argument s is not a socket.

20 [EFAULT] An invalid user space address was specified for a parameter.

20 [EMSGSIZE] The socket requires that message be sent atomically, and the size of the message to be sent made this impossible.

20 [EWOULDBLOCK] The socket is marked non-blocking and the requested operation would block.

20 [ENOBUFS] The system was unable to allocate an internal buffer. The operation may succeed when buffers become available.

20 [ENOBUFS] The output queue for a network interface was full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion.

fcntl(2), recv(2), select(2), getsockopt(2), socket(2), write(2)