blocks|key|1631338|text|这里有一种使用可变模板和std::make_index_sequence的方法|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1631339|#include+<utility>

template<typename+T>+struct+blank_array;
template<std::size_t...+Is>
struct+blank_array<std::integer_sequence<std::size_t,+Is...>>+{
++++static+constexpr+char+arr[]+=+{(Is,+'+')...,+'\0'};
};
template<std::size_t...+Is>
constexpr+char+blank_array<std::integer_sequence<std::size_t,+Is...>>::arr[];

template<std::size_t+N>
constexpr+const+char+(&blanks)[N%2B1]+=
++++blank_array<std::make_index_sequence<N>>::arr;|code-block|syntax|javascript|1631340|示例用法：|1631341|#include+<iostream>

int+main()
{
++++std::cout+<<+"["+<<+blanks<5>+<<+"]\n";
}|1631342|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/utility/integer_sequence^0|C|O|C|O|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

Here's a way to do it using variadic templates and <a href="http://en.cppreference.com/w/cpp/utility/integer_sequence" rel="nofollow noreferrer"><code>std::make_index_sequence</code></a>:

<pre><code>#include &lt;utility&gt;

template&lt;typename T&gt; struct blank_array;
template&lt;std::size_t... Is&gt;
struct blank_array&lt;std::integer_sequence&lt;std::size_t, Is...&gt;&gt; {
 static constexpr char arr[] = {(Is, ' ')..., '\0'};
};
template&lt;std::size_t... Is&gt;
constexpr char blank_array&lt;std::integer_sequence&lt;std::size_t, Is...&gt;&gt;::arr[];

template&lt;std::size_t N&gt;
constexpr const char (&amp;blanks)[N+1] =
 blank_array&lt;std::make_index_sequence&lt;N&gt;&gt;::arr;
</code></pre>

Example usage:

<pre><code>#include &lt;iostream&gt;

int main()
{
 std::cout &lt;&lt; "[" &lt;&lt; blanks&lt;5&gt; &lt;&lt; "]\n";
}
</code></pre>

blocks|key|1631334|text|通过一些实验，我发现可以使用更强大的constexpr语句在c%2B%2B14或更高版本中实现这一点。在这种情况下，使用递归模板。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1631335|#include+<cstdio>
#include+<array>

template<size_t+arrsize,+size_t+setnum>
constexpr+void+initVal(std::array<char,+arrsize>+&tmp)+{
+++std::get<setnum>(tmp)+=+'+';
+++if+(setnum)+initVal<arrsize,+setnum+?+setnum+-+1+:+0>(tmp);
}

template<size_t+arrsize>
constexpr+auto+initArray()+->+std::array<char,+arrsize>+{
+++std::array<char,+arrsize>+tmp{};
+++std::get<arrsize+-+1>(tmp)+=+'\0';
+++initVal<arrsize,+arrsize+-+2>(tmp);
+++return+tmp;
}

constexpr+std::array<char,+5+%2B+1>+globalArr+=+initArray<5+%2B+1>();

int+main()
{
+++puts(globalArr.data());
}|code-block|syntax|javascript|1631336|entityMap^0|I|9|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

I figured out with some experimentation you can do this in c++14 or above using the more powerful <code>constexpr</code> statements. In this case using a recursive template.

<pre><code>#include &lt;cstdio&gt;
#include &lt;array&gt;

template&lt;size_t arrsize, size_t setnum&gt;
constexpr void initVal(std::array&lt;char, arrsize&gt; &amp;tmp) {
 std::get&lt;setnum&gt;(tmp) = ' ';
 if (setnum) initVal&lt;arrsize, setnum ? setnum - 1 : 0&gt;(tmp);
}

template&lt;size_t arrsize&gt;
constexpr auto initArray() -&gt; std::array&lt;char, arrsize&gt; {
 std::array&lt;char, arrsize&gt; tmp{};
 std::get&lt;arrsize - 1&gt;(tmp) = '\0';
 initVal&lt;arrsize, arrsize - 2&gt;(tmp);
 return tmp;
}

constexpr std::array&lt;char, 5 + 1&gt; globalArr = initArray&lt;5 + 1&gt;();

int main()
{
 puts(globalArr.data());
}
</code></pre>

blocks|key|1211096|text|谢谢大家。我对你的几个回复投了赞成票并将其标记为答案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1211097|我想我希望的是更简单的东西。这并不是世界上最重要的编程要求；我只是想，也许我错过了一种简单的方式来实现这一点。你的答案很棒！|1211098|我决定最简单的事情是颠倒这个问题:让编码器指定一个所需长度的字符串，并从中推导出长度：|1211099|//+Fill+the+following+blanks+array+to+a+length+equal+to+the+minimum+number+of+blanks+to+find+(minimum+2)
//++++++++++++++++++++++++++++12345678901234567890
static+const+char+blanks[]+=+"+++++";
static+const+int+numBlanks+=+sizeof(blanks)-1;|code-block|syntax|javascript|1211100|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Thanks all. I upvoted and marked as answers several of your replies.

I guess I was hoping for something simpler. This is not the most important programming requirement in the world; I just thought perhaps I was missing a straightforward way of doing this. Your answers are great!

I decided the simplest thing was to reverse the problem: have the coder specify a string of the desired length and derive the length from that:

<pre><code>// Fill the following blanks array to a length equal to the minimum number of blanks to find (minimum 2)
// 12345678901234567890
static const char blanks[] = " ";
static const int numBlanks = sizeof(blanks)-1;
</code></pre>

I would like to define a string (char array) of ASCII blanks exactly as long as some static const int or macro. I want it to happen at compile time, not run time.

For example, if 

<pre><code>static const int numBlanks = 5
</code></pre>

then 

<pre><code>char foo[] = " " 
</code></pre>

(five blanks) 

and if 

<pre><code>numBlanks = 3 
</code></pre>

then 

<pre><code>char foo[] = " " 
</code></pre>

(three blanks) 

and so forth. (Why? I want to use it with <code>strstr()</code> to locate a sequence of at least <code>numBlanks</code>, with <code>numBlanks</code> setable at compile time.)

Yes, you do it with <code>new</code>, <code>memset()</code> and a <code>/0</code>, but I want to do it once at compile time, not again and again at run time.

Yes, I could come pretty close with 

<pre><code>char foo[] = " "; 
foo[numBlanks] = '\0'; 
</code></pre>

and a comment or <code>assert()</code> to make sure <code>numBlanks</code> was never greater than the compiled length of <code>foo</code>.

But can I do this all at compile time? Define a char array of all blanks exactly numBlanks long, where <code>numBlanks</code> is a C++ static const int or a macro?

How define array of blanks of C++ compile time defined length?

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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我想定义一个ASCII空格的字符串(char数组)，和一些静态常量、int或宏一样长。我希望它发生在编译时，而不是运行时。例如，如果static const int numBlanks = 5然后char foo[] = "     " (五个空格)如果numBlanks = 3 然后char foo[] = "   ...

问如何定义C++编译时定义长度的空格数组？
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问如何定义C++编译时定义长度的空格数组？EN