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📁 IBM SOCKET 教程。LINUX环境下SOCKET学习的教程。
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>receive/send 循环</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 4 页（共4 页）</nobr></font></td>
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<font size="2" face="Verdana, Arial, Helvetica">
<p>UDP 服务器中的重大举措是它的主循环 —— 虽然也不过如此。基本上，我们是在一个 <code>recvfrom()</code> 调用中永久地等待接收一条消息。此时，<code>echoclient</code> 结构将使用连接的 socket 的相关成员来填充。  然后我们在后续的 <code>sendto()</code> 调用中使用该结构。</p>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
            /* Run until cancelled */
            while (1) {
              /* Receive a message from the client */
              clientlen = sizeof(echoclient);
              if ((received = recvfrom(sock, buffer, BUFFSIZE, 0,
                                       (struct sockaddr *) &amp;echoclient,
                                       &amp;clientlen)) &lt; 0) {
                Die("Failed to receive message");
              }
              fprintf(stderr,
                      "Client connected: %s\n", inet_ntoa(echoclient.sin_addr));
              /* Send the message back to client */
              if (sendto(sock, buffer, received, 0,
                         (struct sockaddr *) &amp;echoclient,
                         sizeof(echoclient)) != received) {
                Die("Mismatch in number of echo'd bytes");
              }
            }
          }
          </code>
</pre>
<p>大功告成！我们可以不断地接收和发送消息，同时在此过程中向控制台报告连接情况。当然，正如我们将在下一节看到的，这种安排一次仅做一件事情，这对于处理许多客户机的服务器来说可能是一个问题（对这个简单的 echo 服务器来说或许不是问题，但是更复杂的情况可能会引入糟糕的延迟）。 </p>
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