www.LinuxHowtos.org
SEND
Section: POSIX Programmer's Manual (3P)Updated: 2013
Index Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAME
send --- send a message on a socketSYNOPSIS
#include <sys/socket.h> ssize_t send(int socket, const void *buffer, size_t length, int flags);
DESCRIPTION
The send() function shall initiate transmission of a message from the specified socket to its peer. The send() function shall send a message only when the socket is connected. If the socket is a connectionless-mode socket, the message shall be sent to the pre-specified peer address. The send() function takes the following arguments:- socket
- Specifies the socket file descriptor.
- buffer
- Points to the buffer containing the message to send.
- length
- Specifies the length of the message in bytes.
- flags
-
Specifies the type of message transmission. Values of this argument are
formed by logically OR'ing zero or more of the following flags:
-
- MSG_EOR
- Terminates a record (if supported by the protocol).
- MSG_OOB
- Sends out-of-band data on sockets that support out-of-band communications. The significance and semantics of out-of-band data are protocol-specific.
- MSG_NOSIGNAL
- Requests not to send the SIGPIPE signal if an attempt to send is made on a stream-oriented socket that is no longer connected. The [EPIPE] error shall still be returned.
-
RETURN VALUE
Upon successful completion, send() shall return the number of bytes sent. Otherwise, -1 shall be returned and errno set to indicate the error.ERRORS
The send() function shall fail if:- EAGAIN or EWOULDBLOCK
-
The socket's file descriptor is marked O_NONBLOCK and the requested operation would block. - EBADF
- The socket argument is not a valid file descriptor.
- ECONNRESET
- A connection was forcibly closed by a peer.
- EDESTADDRREQ
-
The socket is not connection-mode and no peer address is set. - EINTR
- A signal interrupted send() before any data was transmitted.
- EMSGSIZE
- The message is too large to be sent all at once, as the socket requires.
- ENOTCONN
- The socket is not connected.
- ENOTSOCK
- The socket argument does not refer to a socket.
- EOPNOTSUPP
- The socket argument is associated with a socket that does not support one or more of the values set in flags.
- EPIPE
- The socket is shut down for writing, or the socket is connection-mode and is no longer connected. In the latter case, and if the socket is of type SOCK_STREAM or SOCK_SEQPACKET and the MSG_NOSIGNAL flag is not set, the SIGPIPE signal is generated to the calling thread. The send() function may fail if:
- EACCES
- The calling process does not have appropriate privileges.
- EIO
- An I/O error occurred while reading from or writing to the file system.
- ENETDOWN
- The local network interface used to reach the destination is down.
- ENETUNREACH
-
No route to the network is present. - ENOBUFS
- Insufficient resources were available in the system to perform the operation.
The following sections are informative.
EXAMPLES
None.APPLICATION USAGE
If the socket argument refers to a connection-mode socket, the send() function is equivalent to sendto() (with any value for the dest_addr and dest_len arguments, as they are ignored in this case). If the socket argument refers to a socket and the flags argument is 0, the send() function is equivalent to write().RATIONALE
None.FUTURE DIRECTIONS
None.SEE ALSO
connect(), getsockopt(), poll(), pselect(), recv(), recvfrom(), recvmsg(), sendmsg(), sendto(), setsockopt(), shutdown(), socket(), write() The Base Definitions volume of POSIX.1-2008, <sys_socket.h>COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .