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| <h4 class="subsection">16.8.3 Socket Pairs</h4> |
| |
| <p><a name="index-creating-a-socket-pair-1783"></a><a name="index-socket-pair-1784"></a><a name="index-opening-a-socket-pair-1785"></a> |
| <a name="index-sys_002fsocket_002eh-1786"></a>A <dfn>socket pair</dfn> consists of a pair of connected (but unnamed) |
| sockets. It is very similar to a pipe and is used in much the same |
| way. Socket pairs are created with the <code>socketpair</code> function, |
| declared in <samp><span class="file">sys/socket.h</span></samp>. A socket pair is much like a pipe; the |
| main difference is that the socket pair is bidirectional, whereas the |
| pipe has one input-only end and one output-only end (see <a href="Pipes-and-FIFOs.html#Pipes-and-FIFOs">Pipes and FIFOs</a>). |
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| <!-- sys/socket.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>socketpair</b> (<var>int namespace, int style, int protocol, int filedes</var><tt>[2]</tt>)<var><a name="index-socketpair-1787"></a></var><br> |
| <blockquote><p>This function creates a socket pair, returning the file descriptors in |
| <var>filedes</var><code>[0]</code> and <var>filedes</var><code>[1]</code>. The socket pair |
| is a full-duplex communications channel, so that both reading and writing |
| may be performed at either end. |
| |
| <p>The <var>namespace</var>, <var>style</var> and <var>protocol</var> arguments are |
| interpreted as for the <code>socket</code> function. <var>style</var> should be |
| one of the communication styles listed in <a href="Communication-Styles.html#Communication-Styles">Communication Styles</a>. |
| The <var>namespace</var> argument specifies the namespace, which must be |
| <code>AF_LOCAL</code> (see <a href="Local-Namespace.html#Local-Namespace">Local Namespace</a>); <var>protocol</var> specifies the |
| communications protocol, but zero is the only meaningful value. |
| |
| <p>If <var>style</var> specifies a connectionless communication style, then |
| the two sockets you get are not <em>connected</em>, strictly speaking, |
| but each of them knows the other as the default destination address, |
| so they can send packets to each other. |
| |
| <p>The <code>socketpair</code> function returns <code>0</code> on success and <code>-1</code> |
| on failure. The following <code>errno</code> error conditions are defined |
| for this function: |
| |
| <dl> |
| <dt><code>EMFILE</code><dd>The process has too many file descriptors open. |
| |
| <br><dt><code>EAFNOSUPPORT</code><dd>The specified namespace is not supported. |
| |
| <br><dt><code>EPROTONOSUPPORT</code><dd>The specified protocol is not supported. |
| |
| <br><dt><code>EOPNOTSUPP</code><dd>The specified protocol does not support the creation of socket pairs. |
| </dl> |
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