SEND(2) BSD System Calls Manual SEND(2)
send, sendto, sendmsg -- send a message from a socket
send(int s, const void *msg, size_t len, int flags);
sendto(int s, const void *msg, size_t len, int flags, const struct sockaddr *to, int tolen);
sendmsg(int s, const 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, the error EMSGSIZE is returned, and the message is not transmitted.
No indication of failure to deliver is implicit in a send(). Locally detected errors are indicated by a return value of -1.
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 ``out-of-band'' data on sockets that support this notion (e.g. SOCK_STREAM); the underlying protocol must
also support ``out-of-band'' 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.
Send(), sendto(), and sendmsg() fail if:
[EBADF] An invalid descriptor was specified.
[ENOTSOCK] The argument s is not a socket.
[EFAULT] An invalid user space address was specified for a parameter.
[EMSGSIZE] The socket requires that message be sent atomically, and the size of the message to be sent made this impossible.
[EAGAIN] The socket is marked non-blocking and the requested operation would block.
[ENOBUFS] The system was unable to allocate an internal buffer. The operation may succeed when buffers become available.
[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.
[EACCES] The SO_BROADCAST option is not set on the socket, and a broadcast address was given as the destination.
[EHOSTUNREACH] The destination address specified an unreachable host.
fcntl(2), recv(2), select(2), getsockopt(2), socket(2), write(2)
The send() function call appeared in 4.2BSD.
4.2 Berkeley Distribution February 21, 1994 4.2 Berkeley Distribution