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);
DESCRIPTION
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.
RETURN VALUES
The call returns the number of characters sent, or -1 if an error occurred.
ERRORS
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.
SEE ALSO
fcntl(2), recv(2), select(2), getsockopt(2), socket(2), write(2)
HISTORY
The send function call appeared in
4.2BSD.