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<title>7.14 结构体表达式</title>
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<a href="00860.html" target="topic">第七章 操作符与表达式</a></div>
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7.14 结构体表达式</div>
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结构体表达式（压缩的和非压缩的）可以使用花括号和逗号由成员表达式构建，其中成员表达式以成员声明的顺序排列。复制操作符可以用来设置准确的成员数目。每一个成员表达式应该在对结构体中对应成员类型赋值的关联文中计算。结构体表达式也可以使用成员的名字来构建。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00229"><pre class="Element12"><span style="color: #0000FF">module</span> mod1<span style="color: #800080">;</span>

<span style="color: #0000FF">typedef</span> <span style="color: #0000FF">struct</span> <span style="color: #800080">{</span>
    <span style="color: #0000FF">int</span> x<span style="color: #800080">;</span>
    <span style="color: #0000FF">int</span> y<span style="color: #800080">;</span>
<span style="color: #800080">}</span> st<span style="color: #800080">;</span>

st s1<span style="color: #800080">;</span>

<span style="color: #0000FF">int</span> k <span style="color: #800080">=</span> <span style="color: #FF0000">1</span><span style="color: #800080">;</span>

<span style="color: #0000FF">initial begin</span>
    <span style="color: #800080">#</span><span style="color: #FF0000">1</span> s1 <span style="color: #800080">=</span> <span style="color: #800080">{</span>1<span style="color: #800080">,</span> 2<span style="color: #800080">+</span>k<span style="color: #800080">};</span>     <span style="color: #008000">// 通过位置构建结构体表达式</span>
    <span style="color: #800080">#</span><span style="color: #FF0000">1</span> <span style="color: #0000FF">$display</span><span style="color: #800080">(</span>s1<span style="color: #800080">.</span>x<span style="color: #800080">,</span> s1<span style="color: #800080">.</span>y<span style="color: #800080">);</span>
    <span style="color: #800080">#</span><span style="color: #FF0000">1</span> s1 <span style="color: #800080">= {</span>x<span style="color: #800080">:</span><span style="color: #FF0000">2</span>, y<span style="color: #800080">:</span><span style="color: #FF0000">3</span><span style="color: #800080">+</span>k<span style="color: #800080">};</span> <span style="color: #008000">// 通过名字构建结构体表达式</span>
    <span style="color: #800080">#</span><span style="color: #FF0000">1</span> <span style="color: #0000FF">$display</span><span style="color: #800080">(</span>s1<span style="color: #800080">);</span>
    <span style="color: #800080">#</span><span style="color: #FF0000">1</span> <span style="color: #0000FF">$finish</span><span style="color: #800080">;</span>
<span style="color: #0000FF">end</span>

<span style="color: #0000FF">endmodule</span></pre></div></div>
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有时我们希望将结构体成员设置成某一个值而无需知道结构体到底有多少个成员或者成员的具体名字是什么。这种方式可以使用<span style="color: #0000FF">default</span>关键字来实现： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00230"><pre class="Element12"><span style="color: #0000FF">initial</span> s1 <span style="color: #800080">= {</span><span style="color: #0000FF">default</span><span style="color: #800080">:</span><span style="color: #FF0000">2</span><span style="color: #800080">};</span> <span style="color: #008000">// 将x和y设置成2</span></pre></div></div>
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我们也可以使用<span style="color: #800080">{<i></span>member<span style="color: #800080"></i>:<i></span>value<span style="color: #800080"></i>}</span>或<span style="color: #800080">{<i></span>data_type<span style="color: #800080"></i>:</span> <i>default_value<span style="color: #800080"></i>}</span>这样的语法： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00231"><pre class="Element12">ab abkey<span style="color: #800080">[</span><span style="color: #FF0000">1</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">] = {{</span>a<span style="color: #800080">:</span><span style="color: #FF0000">1</span><span style="color: #800080">, </span>b<span style="color: #800080">:</span><span style="color: #FF0000">1.0</span><span style="color: #800080">}, {</span><span style="color: #0000FF">int</span><span style="color: #800080">:</span><span style="color: #FF0000">2</span><span style="color: #800080">, </span><span style="color: #0000FF">shortreal</span><span style="color: #800080">:</span><span style="color: #FF0000">2.0</span><span style="color: #800080">}};</span></pre></div></div>
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注意：<span style="color: #0000FF">default</span>关键字可以应用于嵌套结构体中的成员或结构体中非压缩数组的元素。事实上，它可以沿着嵌套深入到其中的内建类型或压缩数组。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00232"><pre class="Element12"><span style="color: #0000FF">struct</span> <span style="color: #800080">{</span>
    <span style="color: #0000FF">int</span> A<span style="color: #800080">;</span>
    <span style="color: #0000FF">struct</span> <span style="color: #800080">{</span>
        <span style="color: #0000FF">int</span> B<span style="color: #800080">,</span> C<span style="color: #800080">;</span>
    <span style="color: #800080">}</span> BC1<span style="color: #800080">,</span> BC2<span style="color: #800080">;</span>
<span style="color: #800080">}</span>

ABC <span style="color: #800080">=</span> <span style="color: #800080">{</span>A<span style="color: #800080">:</span><span style="color: #FF0000">1</span><span style="color: #800080">,</span> BC1<span style="color: #800080">:{</span>B<span style="color: #800080">:</span><span style="color: #FF0000">2</span><span style="color: #800080">,</span> C<span style="color: #800080">:</span><span style="color: #FF0000">3</span><span style="color: #800080">}</span>, BC2<span style="color: #800080">:{</span>B<span style="color: #800080">:</span><span style="color: #FF0000">4</span><span style="color: #800080">,</span>C<span style="color: #800080">:</span><span style="color: #FF0000">5</span><span style="color: #800080">}};</span>
DEF <span style="color: #800080">=</span> <span style="color: #800080">{</span><span style="color: #0000FF">default</span><span style="color: #800080">:</span><span style="color: #FF0000">10</span><span style="color: #800080">};</span></pre></div></div>
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