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| <h4 class="subsection">16.10.1 Sending Datagrams</h4> |
| |
| <p><a name="index-sending-a-datagram-1818"></a><a name="index-transmitting-datagrams-1819"></a><a name="index-datagrams_002c-transmitting-1820"></a> |
| <a name="index-sys_002fsocket_002eh-1821"></a>The normal way of sending data on a datagram socket is by using the |
| <code>sendto</code> function, declared in <samp><span class="file">sys/socket.h</span></samp>. |
| |
| <p>You can call <code>connect</code> on a datagram socket, but this only |
| specifies a default destination for further data transmission on the |
| socket. When a socket has a default destination you can use |
| <code>send</code> (see <a href="Sending-Data.html#Sending-Data">Sending Data</a>) or even <code>write</code> (see <a href="I_002fO-Primitives.html#I_002fO-Primitives">I/O Primitives</a>) to send a packet there. You can cancel the default |
| destination by calling <code>connect</code> using an address format of |
| <code>AF_UNSPEC</code> in the <var>addr</var> argument. See <a href="Connecting.html#Connecting">Connecting</a>, for |
| more information about the <code>connect</code> function. |
| |
| <!-- sys/socket.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>sendto</b> (<var>int socket, void *buffer. size_t size, int flags, struct sockaddr *addr, socklen_t length</var>)<var><a name="index-sendto-1822"></a></var><br> |
| <blockquote><p>The <code>sendto</code> function transmits the data in the <var>buffer</var> |
| through the socket <var>socket</var> to the destination address specified |
| by the <var>addr</var> and <var>length</var> arguments. The <var>size</var> argument |
| specifies the number of bytes to be transmitted. |
| |
| <p>The <var>flags</var> are interpreted the same way as for <code>send</code>; see |
| <a href="Socket-Data-Options.html#Socket-Data-Options">Socket Data Options</a>. |
| |
| <p>The return value and error conditions are also the same as for |
| <code>send</code>, but you cannot rely on the system to detect errors and |
| report them; the most common error is that the packet is lost or there |
| is no-one at the specified address to receive it, and the operating |
| system on your machine usually does not know this. |
| |
| <p>It is also possible for one call to <code>sendto</code> to report an error |
| owing to a problem related to a previous call. |
| |
| <p>This function is defined as a cancellation point in multi-threaded |
| programs, so one has to be prepared for this and make sure that |
| allocated resources (like memory, files descriptors, semaphores or |
| whatever) are freed even if the thread is canceled. |
| <!-- @xref{pthread_cleanup_push}, for a method how to do this. --> |
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