SEND(2) BSD System Calls Manual SEND(2)NAME
send, sendto, sendmsg — send a message from a socket
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
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);
DESCRIPTIONSend(), 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 sup‐
port this notion (e.g. SOCK_STREAM); the underlying protocol must also
support “out-of-band” data. MSG_DONTROUTE is usually used only by diag‐
nostic or routing programs.
See recv(2) for a description of the msghdr structure.
RETURN VALUES
The call returns the number of characters sent, or -1 if an error
occurred.
ERRORSSend(), 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 avail‐
able.
[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 con‐
gestion.
[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.
SEE ALSOfcntl(2), recv(2), select(2), getsockopt(2), socket(2), write(2)HISTORY
The send() function call appeared in 4.2BSD.
4.2 Berkeley Distribution February 21, 1994 4.2 Berkeley Distribution
