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# send

    SEND(2)                       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, socklen_t 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) or poll(2) system calls
         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 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.

         [EINVAL]           The flags parameter is invalid.

         [EHOSTDOWN]        The destination address specified a host that is down.

         [ENETDOWN]         The destination address specified a network that is
                            down.

         [ECONNREFUSED]     The destination host rejected the message (or a previ-
                            ous one).  This error can only be returned by con-
                            nected sockets.

         [ENOPROTOOPT]      There was a problem sending the message.  This error
                            can only be returned by connected sockets.

         [EDESTADDRREQ]     The socket is not connected, and no destination
                            address was specified.

         [EISCONN]          The socket is already connected, and a destination
                            address was specified.

         In addition, send() and sendto() may return the following error:

         [EINVAL]           len was larger than SSIZE_MAX.

         Also, sendmsg() may return the following errors:

         [EINVAL]           The sum of the iov_len values in the msg_iov array
                            overflowed an ssize_t.

         [EMSGSIZE]         The msg_iovlen member of msg was less than 0 or larger
                            than IOV_MAX.

         [EAFNOSUPPORT]     Addresses in the specified address family cannot be
                            used with this socket.

    SEE ALSO
         fcntl(2), getsockopt(2), poll(2), recv(2), select(2), poll(2), socket(2),
         write(2)

    HISTORY
         The send() function call appeared in 4.2BSD.

    BSD                              July 28, 1998                             BSD

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