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4.14 队列</div>
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队列是一个相同元素的可变尺寸的有序集合。队列能够以常量时间访问它的所有元素，也能够以常量时间在队列的尾部和头部插入和删除元素。队列中的每一个元素都通过一个序号来标识，这个序号代表了元素在队列内的位置，<span style="color: #FF0000">0</span>代表第一个元素，<span style="color: #FF0000">$</span>代表最后一个元素。队列类似于一个一维的非压缩数组，它可以自动地增长和缩减。因此，与数组一样，队列可以使用索引、串联、分片、相等操作符进行处理。 </p>
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队列使用与非压缩数组相同的语法声明，但可以使用<span style="color: #FF0000">$</span>作为数组尺寸。队列的尺寸可以通过指定可选的右边界（最后一个索引）进行限制。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00163"><pre class="Element12">variable_dimension ::= <span style="color: #008000">// 引用自附录A.2.5</span>
{sized_or_unsized_dimension}
| associative_dimension
| queue_dimension
queue_dimension ::= <strong><span style="color: #FF0000">[$</span></strong>[<strong><span style="color: #FF0000">:</span></strong>constant_expression]<strong><span style="color: #FF0000">]</span></strong></pre></div></div>
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<strong>语法4-3—队列维数的声明（摘录自附录A）</strong></p><p class="Element10">
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<i>constant_expression</i>必须能够计算成一个正的整数值 </p>
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例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00164"><pre class="Element12"><span style="color: #0000FF">byte</span> q1<span style="color: #800080">[</span><span style="color: #FF0000">$</span><span style="color: #800080">];</span> <span style="color: #008000">// 一个字节队列</span>
<span style="color: #0000FF">string</span> names<span style="color: #800080">[</span><span style="color: #FF0000">$</span><span style="color: #800080">]</span> <span style="color: #800080">= {</span><span style="color: #575D94">"Bob"</span><span style="color: #800080">};</span> <span style="color: #008000">// 具有一个元素的字符串队列</span>
<span style="color: #0000FF">integer</span> Q<span style="color: #800080">[</span><span style="color: #FF0000">$</span><span style="color: #800080">]</span> <span style="color: #800080">= {</span><span style="color: #FF0000">3</span><span style="color: #800080">,</span> <span style="color: #FF0000">2</span><span style="color: #800080">,</span> <span style="color: #FF0000">7</span><span style="color: #800080">};</span> <span style="color: #008000">// 一个被初始化成三个元素的整数队列</span>
<span style="color: #0000FF">bit</span> q2<span style="color: #800080">[</span><span style="color: #FF0000">$</span><span style="color: #800080">:</span><span style="color: #FF0000">255</span><span style="color: #800080">];</span> <span style="color: #008000">// 一个最大尺寸为256的位队列</span></pre></div></div>
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空队列文本<span style="color: #800080">{}</span>可以用来指示一个空队列。如果声明时没有提供初始值，那么队列变量被初始化成一个空队列。</p></div>
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描述 </div></td></tr><tr>
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<a href="00508.html" target="topic">4.14.1 队列操作符</a> </div></td><td class="Element206" valign="top" width="50%">
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队列可以与非压缩数组执行相同的操作，除下述的操作符和操作规则外，它们使用相同的操作符和操作规则。 </div></td></tr><tr>
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<a href="00509.html" target="topic">4.14.2 队列方法</a> </div></td><td class="Element206" valign="top" width="50%">
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除了数组操作符外，队列还提供了几个内建方法。 </div></td></tr></table></div></div>
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