send(), sendto(), and sendmsg() are used to transmit a message to another transport end-point. send() may be used only when the socket is in a connected state, while sendto() and sendmsg() may be used at any time. s is a socket created with socket(3SOCKET).

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.

A return value of -1 indicates locally detected errors only. It does not implicitly mean the message was not delivered.

If the socket does not have enough buffer space available to hold the message being sent, send() blocks, unless the socket has been placed in non-blocking I/O mode (see fcntl(2)). The select(3C) or poll(2) call may be used to determine when it is possible to send more data.

The flags parameter is formed from the bitwise OR of zero or more of the following:

MSG_OOB

Send "out-of-band" data on sockets that support this notion. The underlying protocol must also support "out-of-band" data. Only SOCK_STREAM sockets created in the AF_INETand AF_INET address families support out-of-band data.

MSG_DONTROUTE

The SO_DONTROUTE option is turned on for the duration of the operation. It is used only by diagnostic or routing programs.

See recv(3SOCKET) for a description of the msghdr structure.

These calls return the number of bytes sent, or -1 if an error occurred.

The send(), sendto(), and sendmsg() functions will fail if:

EBADF

s is an invalid file descriptor.

EINTR

The operation was interrupted by delivery of a signal before any data could be buffered to be sent.

EMSGSIZE

The socket requires that message be sent atomically, and the message was too long.

ENOMEM

There was insufficient memory available to complete the operation.

ENOSR

There were insufficient STREAMS resources available for the operation to complete.

ENOTSOCK

s is not a socket.

EWOULDBLOCK

The socket is marked non-blocking and the requested operation would block.

The send() and sendto() functions will fail if:

EINVAL

The len argument overflowed a ssize_t.

The sendto() function will fail if:

EINVAL

tolen is not the size of a valid address for the specified address family.

The sendmsg() function will fail if:

EINVAL

Either the msg_iovlen member of the msghdr structure pointed to by msg was less than or equal to 0, or the sum of the iov_len values in the msg_iov array overflowed a ssize_t.

EINVAL

Either one of the iov_len values in the msg_iov array member of the msghdr structure pointed to by msg was negative, or the sum of the iov_len values in the msg_iov array overflowed a ssize_t.

The send() function will fail if:

EPIPE

The socket is shut down for writing, or the socket is connection-mode and is no longer connected. In the latter case, if the socket is of type SOCK_STREAM, the SIGPIPE signal is generated to the calling process.

See attributes(5) for descriptions of the following attributes:

fcntl(2), poll(2), write(2), connect(3SOCKET), getsockopt(3SOCKET), recv(3SOCKET), select(3C), socket(3HEAD), socket(3SOCKET), attributes(5)