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PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
SEND(3P) POSIX Programmer's ManualSEND(3P)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.
send — send a message on a socket
#include <sys/socket.h> ssize_t send(intsocket, const void *buffer, size_tlength, intflags);
Thesend() function shall initiate transmission of a message from the specified socket to its peer. Thesend() 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. Thesend() 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. The length of the message to be sent is specified by thelength argument. If the message is too long to pass through the underlying protocol,send() shall fail and no data shall be transmitted. Successful completion of a call tosend() does not guarantee delivery of the message. A return value of -1 indicates only locally-detected errors. If space is not available at the sending socket to hold the message to be transmitted, and the socket file descriptor does not have O_NONBLOCK set,send() shall block until space is available. If space is not available at the sending socket to hold the message to be transmitted, and the socket file descriptor does have O_NONBLOCK set,send() shall fail. Theselect() andpoll() functions can be used to determine when it is possible to send more data. The socket in use may require the process to have appropriate privileges to use thesend() function.
Upon successful completion,send() shall return the number of bytes sent. Otherwise, -1 shall be returned anderrno set to indicate the error.
Thesend() function shall fail if:EAGAINorEWOULDBLOCK The socket's file descriptor is marked O_NONBLOCK and the requested operation would block.EBADFThesocket 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.EINTRA signal interruptedsend() 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 Thesocket argument does not refer to a socket.EOPNOTSUPP Thesocket argument is associated with a socket that does not support one or more of the values set inflags.EPIPEThe 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. Thesend() function may fail if:EACCESThe calling process does not have appropriate privileges.EIOAn 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.
None.
If thesocket argument refers to a connection-mode socket, thesend() function is equivalent tosendto() (with any value for thedest_addr anddest_len arguments, as they are ignored in this case). If thesocket argument refers to a socket and theflags argument is 0, thesend() function is equivalent towrite().
None.
None.
connect(3p),getsockopt(3p),poll(3p),pselect(3p),recv(3p),recvfrom(3p),recvmsg(3p),sendmsg(3p),sendto(3p),setsockopt(3p),shutdown(3p),socket(3p),write(3p) The Base Definitions volume of POSIX.1‐2017,sys_socket.h(0p)
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 athttp://www.opengroup.org/unix/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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017SEND(3P)Pages that refer to this page:sys_socket.h(0p), connect(3p), recv(3p), recvfrom(3p), recvmsg(3p), sendmsg(3p), sendto(3p), shutdown(3p), socket(3p)
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