blocks|key|586549|text|您要做的是聚合初始化，这意味着sArray和dArray中的元素在未指定时为值初始化。因为short和double是标量类型，这意味着零初始化|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|586550|由于只指定第一个元素，所以所有剩余的元素都将初始化为0|586551|按照注释中的要求，初始化数组的方法是std::fill或std::fill_n|586552|#include+<algorithm>

struct+Nested+{
++++explicit+Nested()+{
++++++++std::fill_n(sArray,+5,+0);
++++++++std::fill_n(dArray,+5,+0.0);
++++}
++++union+{
++++++++short+sArray[5];
++++++++float+fVal;++//+Must+NOT+be+initialized+-+obviously,+only+1+member+of+a
++++++++++++++++++++//+union+can+be
++++};

++++double+dArray[5];
};|code-block|syntax|javascript|586553|通常，我建议使用std::array及其fill函数：|586554|#include+<array>

struct+Nested+{
++++explicit+Nested()+{
++++++++sArray.fill(0);
++++++++dArray.fill(0.0);
++++}
++++union+{
++++++++std::array<short,+5>+sArray;
++++++++float+fVal;++//+Must+NOT+be+initialized+-+obviously,+only+1+member+of+a
++++++++++++++++++++//+union+can+be
++++};

++++std::array<double,+5>+dArray;
};|586555|entityMap|0|LINK|mutability|MUTABLE|url|https://en.cppreference.com/w/cpp/language/aggregate_initialization|1|https://en.cppreference.com/w/cpp/language/value_initialization|2|https://en.cppreference.com/w/cpp/language/zero_initialization^0|F|6|M|6|19|5|1F|6|5|5|0|12|4|1|1V|4|2|0|0|I|9|S|B|0|0|8|A|K|4|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@$9|1D|A|1E|1|1F]|$9|1G|A|1H|1|1I]|$9|1J|A|1K|1|1L]]|E|$]]|$1|F|3|G|5|6|7|1M|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1N|8|@$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1S|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1T|8|@$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1Y|8|@]|D|@]|E|$M|N]]|$1|S|3|-4|5|6|7|1Z|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]|10|$5|V|W|X|E|$Y|11]]|12|$5|V|W|X|E|$Y|13]]]]

What you are doing is <a href="https://en.cppreference.com/w/cpp/language/aggregate_initialization" rel="nofollow noreferrer">aggregate initialization</a>, which means the elements in <code>sArray</code> and <code>dArray</code> are <a href="https://en.cppreference.com/w/cpp/language/value_initialization" rel="nofollow noreferrer">value initialized</a> when not specified. Because <code>short</code> and <code>double</code> are scalar types, this means <a href="https://en.cppreference.com/w/cpp/language/zero_initialization" rel="nofollow noreferrer">zero initialization</a>
Since you don't specify anything but the first element, all remaining elements will be initialized to 0
As requested in the comments, a way to initialize the arrays would be <code>std::fill</code> or <code>std::fill_n</code>:
<pre><code>#include &lt;algorithm&gt;

struct Nested {
 explicit Nested() {
 std::fill_n(sArray, 5, 0);
 std::fill_n(dArray, 5, 0.0);
 }
 union {
 short sArray[5];
 float fVal; // Must NOT be initialized - obviously, only 1 member of a
 // union can be
 };

 double dArray[5];
};
</code></pre>
In general, I would recommend to instead use <code>std::array</code> and its <code>fill</code> function:
<pre><code>#include &lt;array&gt;

struct Nested {
 explicit Nested() {
 sArray.fill(0);
 dArray.fill(0.0);
 }
 union {
 std::array&lt;short, 5&gt; sArray;
 float fVal; // Must NOT be initialized - obviously, only 1 member of a
 // union can be
 };

 std::array&lt;double, 5&gt; dArray;
};
</code></pre>

I am trying to initialize array members at struct declaration in the following struct with nested union &amp; array:
<pre><code>struct Nested
{

 union 
 { 
 short sArray[5] = {42};
 float fVal; // Must NOT be initialized - obviously, only 1 member of a union can be
 };

 double dArray[5] = {77.7};

};
</code></pre>
While the code compiles just fine, only first elements of both arrays are initialized, when running/debugging the code..
sArray[0] is set to 42, remaining elements are all set to 0
dArray[0] is set to 77.69999, remaining are all set to 0
All other answers I found, mention initialization at instance declaration, but not default init in struct/class declaration.
I have not seen/found whether this syntax is enabled (for array members too) by gnu c++17.
However, since it compiles WO warning one would assume it should correct.
Am I doing something wrong ?
Edit:
Or how do I simply initialize my arrays ?

In struct nested union/array member default initialization compiles, but is not happening correctly?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我试图用嵌套的联合和数组在结构声明中初始化数组成员：struct Nested{  union   {      short sArray[5] = {42};    float fVal;  // Must NOT be initialized - obviously, only 1 member of a unio...

在struct中，嵌套的联合/数组成员默认初始化编译，但没有正确发生吗？-腾讯云开发者社区-腾讯云

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