send, sendto, sendmsg - send a message from a socket
cc [ flag... ] file... -lsocket -lnsl [ library... ]
ssize_t send(int s, const void *msg, size_t len, int flags);
ssize_t sendto(int s, const void *msg, size_t len, int flags,
const struct sockaddr *to, int tolen);
ssize_t sendmsg(int s, const struct msghdr *msg, int flags);
The send(), sendto(), and sendmsg() functions are used to
transmit a message to another transport end-point. The send() function
can be used only when the socket is in a connected state. See
connect(3SOCKET). The sendto() and sendmsg() functions
can be used at any time. The s socket is created with
The address of the target is supplied by to with a
tolen parameter used to specify the size. The length of the message
is supplied by the len parameter. For socket types such as
SOCK_DGRAM and SOCK_RAW that require atomic messages, the
error EMSGSIZE is returned and the message is not transmitted when it
is too long to pass atomically through the underlying protocol. The same
restrictions do not apply to SOCK_STREAM sockets.
A return value −1 indicates locally detected errors.
It does not imply a delivery failure.
If the socket does not have enough buffer space available to hold
a message, the send() function blocks the message, unless the socket
has been placed in non-blocking I/O mode (see fcntl(2)). The
select(3C) or poll(2) call can 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:
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_INET or the
AF_INET6 address family support out-of-band data.
The SO_DONTROUTE option is turned on for the
duration of the operation. It is used only by diagnostic or routing
Don't generate the SIGPIPE signal when a
stream-oriented socket is no longer connected.
The sendmsg() function call uses a msghdr structure
defined in <sys/socket.h> to minimize the number of directly
Upon successful completion, these functions return the number of bytes sent.
Otherwise, they return -1 and set errno to indicate the error.
In addition to the errors documented below, an asynchronous error generated by
the underlying socket protocol may be returned. For the full list of errors,
please see the corresponding socket protocol manual page. For example, for a
list of TCP errors, please see tcp(4P).
The send(), sendto(), and sendmsg() functions
return errors under the following conditions:
s is not a valid file descriptor.
The s argument refers to a connection oriented
socket and the connection was forcibly closed by the peer and is no longer
valid. I/O can no longer be performed to filedes.
The operation was interrupted by delivery of a signal
before any data could be buffered to be sent.
The message is too large to be sent all at once (as the
socket requires), or the msg_iovlen member of the msghdr
structure pointed to by message is less than or equal to 0 or is greater than
Insufficient memory is available to complete the
Insufficient STREAMS resources are available for the
operation to complete.
s is not a socket.
The socket is marked non-blocking and the requested
operation would block. EWOULDBLOCK is also returned when sufficient
memory is not immediately available to allocate a suitable buffer. In such a
case, the operation can be retried later.
The requested connection was refused by the peer. For
connected IPv4 and IPv6 datagram sockets, this indicates that the system
received an ICMP Destination Port Unreachable message from the
peer in response to some prior transmission.
The send() and sendto() functions return errors
under the following conditions:
argument overflows a ssize_t
Inconsistent port attributes for system call.
The sendto() function returns errors under the following
The value specified for the tolen parameter is not
the size of a valid address for the specified address family.
A destination address was specified and the socket is
The sendmsg() function returns errors under the following
member of the msghdr
structure pointed to by msg
is less than or equal to 0
, or the
sum of the iov_len
values in the msg_iov
array overflows a
One of the iov_len values in the msg_iov array
member of the msghdr structure pointed to by msg is negative,
or the sum of the iov_len values in the msg_iov array
overflows a ssize_t.
msg_iov contents are inconsistent with port attributes.
The send() function returns errors under the following
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 thread unless the MSG_NOSIGNAL flag is set.
See attributes(7) for descriptions of the following attributes:
fcntl(2), poll(2), write(2), select(3C),
socket.h(3HEAD), connect(3SOCKET), getsockopt(3SOCKET),
recv(3SOCKET), sockaddr(3SOCKET), socket(3SOCKET),