📄 sendmsg.html

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>sendmsg</title></head><body bgcolor=white><center><font size=2>The Single UNIX &reg; Specification, Version 2<br>Copyright &copy; 1997 The Open Group</font></center><hr size=2 noshade><h4>NAME</h4><blockquote>sendmsg - send a message on a socket using a message structure</blockquote><h4>SYNOPSIS</h4><blockquote><pre><code>#include &lt;<a href="syssocket.h.html">sys/socket.h</a>&gt;ssize_t sendmsg (int <I>socket</I>, const struct msghdr *<I>message</I>, int <I>flags</I>);</code></pre></blockquote><h4>DESCRIPTION</h4><blockquote>The<i>sendmsg()</i>function sends a message through a connection-mode or connectionless-modesocket.  If the socket is connectionless-mode, the message will be sent to theaddress specified by <I>msghdr</I>.  If the socket is connection-mode, thedestination address in <I>msghdr</I> is ignored.<p>The function takes the following arguments:<dl compact><dt><I>socket</I><dd>Specifies the socket file descriptor.<dt><I>message</I><dd>Points to a <B>msghdr</B> structure, containing both the destinationaddress and the buffers for the outgoing message.The length and format of the address depend on the addressfamily of the socket.  The <B>msg_flags</B> member is ignored.<dt><I>flags</I><dd>Specifies the type of message transmission.The application may specify 0 or the following flag:<dl compact><dt>MSG_EOR<dd>Terminates a record (if supported by the protocol)<dt>MSG_OOB<dd>Sends out-of-band data on sockets that support out-of-bound data.The significance and semantics of out-of-band data are protocol-specific.</dl><p></dl><p>The <I>msg_iov</I>and <I>msg_iovlen</I>fields of message specifyzero or more buffers containing the data to be sent.<I>msg_iov</I>points to an array of <B>iovec</B>structures; <I>msg_iovlen</I>must be set to the dimension of this array.In each <B>iovec</B>structure, the <I>iov_base</I>field specifies a storage area and the <I>iov_len</I>field gives its size in bytes. Some of these sizes can be zero. The datafrom each storage area indicated by <I>msg_iov</I>is sent in turn.<p>Successful completion of a call to<i>sendmsg()</i>does not guarantee delivery of the message.A return value of -1 indicates only locally-detected errors.<p>If space is not available at the sending socket to hold the message to betransmitted and the socket file descriptor does not have O_NONBLOCK set,<i>sendmsg()</i>function blocks until space is available.  If space is not available at thesending socket to hold the message to be transmitted and the socket filedescriptor does have O_NONBLOCK set,<i>sendmsg()</i>function will fail.<p>If the socket protocol supports broadcast and the specified addressis a broadcast address for the socket protocol,<i>sendmsg()</i>will fail if the SO_BROADCAST option is not set for the socket.<p>The socket in use may require the process to have appropriateprivileges to use the<i>sendmsg()</i>function.</blockquote><h4>RETURN VALUE</h4><blockquote>Upon successful completion,<i>sendmsg()</i>function returns the number of bytes sent.  Otherwise, -1is returned and <I>errno</I> is set to indicate the error.</blockquote><h4>ERRORS</h4><blockquote>The<i>sendmsg()</i>function will fail if:<dl compact><dt>[EAGAIN] or [EWOULDBLOCK]<dd><br>The socket's file descriptor is marked O_NONBLOCK and the requested operationwould block.<dt>[EAFNOSUPPORT]<dd>Addresses in the specified address family cannot be used with this socket.<dt>[EBADF]<dd>The <I>socket</I> argument is not a valid file descriptor.<dt>[ECONNRESET]<dd>A connection was forcibly closed by a peer.<dt>[EFAULT]<dd>The <I>message</I>parameter, or storage pointed to by the <I>msg_name</I>,<I>msg_control</I>or <I>msg_iov</I>fields of the <I>message</I>parameter, or storage pointed to by the<B>iovec</B>structures pointed to by the <I>msg_iov</I>field can not be accessed.<dt>[EINTR]<dd>A signal interrupted<i>sendmsg()</i>before any data was transmitted.<dt>[EINVAL]<dd>The sum of the <B>iov_len</B> values overflows an <B>ssize_t</B>.<dt>[EMSGSIZE]<dd>The message is to large to be sent all at once (as the socketrequires), or the<B>msg_iovlen</B>member of the<B>msghdr</B>structure pointed to by<I>message</I>is less than or equal to 0 or is greater than {IOV_MAX}.<dt>[ENOTCONN]<dd>The socket is connection-mode but is not connected.<dt>[ENOTSOCK]<dd>The <I>socket</I> argument does not refer a socket.<dt>[EOPNOTSUPP]<dd>The <I>socket</I> argument is associated with a socket that does notsupport one or more of the values set in <I>flags</I>.<dt>[EPIPE]<dd>The socket is shut down for writing, or the socket isconnection-mode and is no longer connected.In the latter case, and if the socket is of type SOCK_STREAM, the SIGPIPEsignal is generated to the calling process.</dl><p>If the address family of the socket is AF_UNIX, then<i>sendmsg()</i>will fail if:<dl compact><dt>[EIO]<dd>An I/O error occurred while reading from or writing to the file system.<dt>[ELOOP]<dd>Too many symbolic links were encountered in translating the pathname in thesocket address.<dt>[ENAMETOOLONG]<dd>A component of a pathname exceeded {NAME_MAX} characters, or an entirepathname exceeded {PATH_MAX} characters.<dt>[ENOENT]<dd>A component of the pathname does not name an existing file or the pathname isan empty string.<dt>[ENOTDIR]<dd>A component of the path prefix of the pathname in the socket address is not adirectory.</dl><p>The<i>sendmsg()</i>function may fail if:<dl compact><dt>[EACCES]<dd>Search permission is denied for a component of the path prefix;or write access to the named socket is denied.<dt>[EDESTADDRREQ]<dd>The socket is not connection-mode and does not have its peer address set,and no destination address was specified.<dt>[EHOSTUNREACH]<dd>The destination host cannot be reached (probably because the host is down ora remote router cannot reach it).<dt>[EIO]<dd>An I/O error occurred while reading from or writing to the file system.<dt>[EISCONN]<dd>A destination address was specified and the socketis already connected.<dt>[ENETDOWN]<dd>The local interface used to reach the destination is down.<dt>[ENETUNREACH]<dd>No route to the network is present.<dt>[ENOBUFS]<dd>Insufficient resources were available in the system to perform the operation.<dt>[ENOMEM]<dd>Insufficient memory was available to fulfill the request.<dt>[ENOSR]<dd>There were insufficient STREAMS resources available for the operation tocomplete.</dl><br><p>If the address family of the socket is AF_UNIX, then<i>sendmsg()</i>may fail if:<dl compact><dt>[ENAMETOOLONG]<dd>Pathname resolution of a symbolic link produced an intermediate result whoselength exceeds {PATH_MAX}.</dl></blockquote><h4>APPLICATION USAGE</h4><blockquote>The<i><a href="select.html">select()</a></i>and<i><a href="poll.html">poll()</a></i>functions can be used to determine when it is possible to send more data.</blockquote><h4>SEE ALSO</h4><blockquote><i><a href="getsockopt.html">getsockopt()</a></i>,<i><a href="poll.html">poll()</a></i><i><a href="recv.html">recv()</a></i>,<i><a href="recvfrom.html">recvfrom()</a></i>,<i><a href="recvmsg.html">recvmsg()</a></i>,<i><a href="select.html">select()</a></i>,<i><a href="send.html">send()</a></i>,<i><a href="sendto.html">sendto()</a></i>,<i><a href="setsockopt.html">setsockopt()</a></i>,<i><a href="shutdown.html">shutdown()</a></i>,<i><a href="socket.html">socket()</a></i>,<i><a href="syssocket.h.html">&lt;sys/socket.h&gt;</a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX &reg; is a registered Trademark of The Open Group.<br>Copyright &copy; 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>
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