4.2BSD/usr/man/man2/send.2

.TH SEND 2 "20 September 1983"
.UC 4
.SH NAME
send, sendto, sendmsg \- send a message from a socket
.SH SYNOPSIS
.nf
.ft B
#include <sys/types.h>
#include <sys/socket.h>
.PP
.ft B
cc = send(s, msg, len, flags)
int cc, s;
char *msg;
int len, flags;
.PP
.ft B
cc = sendto(s, msg, len, flags, to, tolen)
int cc, s;
char *msg;
int len, flags;
struct sockaddr *to;
int tolen;
.PP
.ft B
cc = sendmsg(s, msg, flags)
int cc, s;
struct msghdr msg[];
int flags;
.fi
.SH DESCRIPTION
.IR Send ,
.IR sendto ,
and
.I sendmsg
are used to transmit a message to another socket.
.I Send
may be used only when the socket is in a 
.I connected
state, while 
.I sendto
and
.I sendmsg
may be used at any time.
.PP
The address of the target is given by
.I to
with 
.I tolen
specifying its size.
The length of the message is given by
.IR 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.
.PP
No indication of failure to deliver is implicit in a
.IR send .
Return values of \-1 indicate some locally detected errors.
.PP
If no messages space is available at the socket to hold
the message to be transmitted, then
.I send
normally blocks, unless the socket has been placed in
non-blocking i/o mode.
The
.IR select (2)
call may be used to determine when it is possible to
send more data.
.PP
The
.I flags
parameter may be set to SOF_OOB to send \*(lqout-of-band\*(rq
data on sockets which support this notion (e.g. SOCK_STREAM).
.PP
See 
.IR recv (2)
for a description of the
.I msghdr
structure.
.SH "RETURN VALUE
The call returns the number of characters sent, or \-1
if an error occurred.
.SH "ERRORS
.TP 20
[EBADF]
An invalid descriptor was specified.
.TP 20
[ENOTSOCK]
The argument \fIs\fP is not a socket.
.TP 20
[EFAULT]
An invalid user space address was specified for a parameter.
.TP 20
[EMSGSIZE]
The socket requires that message be sent atomically,
and the size of the message to be sent made this impossible.
.TP 20
[EWOULDBLOCK]
The socket is marked non-blocking and the requested operation
would block.
.SH SEE ALSO
recv(2), socket(2)