blocks|key|4803174|text|std::unordered_set使用散列来唯一地标识对象。它使用std::hash<>结构计算散列。这对于原语或STL容器来说是很好的，因为它们已经为它们定义了一个散列结构。但就您的情况而言，没有用于生成散列的散列结构。错误告诉我们：std::__1::hash<coor>。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4803175|为了解决这个问题，我们需要为coor实现一个std::hash<>。|4803176|namespace+std+{
++++template<>
++++struct+hash<coor>+{
++++++++const+size_t+operator()(const+coor&+c)+const
++++++++{
++++++++++++return+std::hash<int>()(c.x)+%5E+std::hash<int>()(c.y);+++
++++++++}
++++};
}|code-block|syntax|javascript|4803177|现在，std::unordered_set有了计算散列所需的散列结构。|4803178|entityMap^0|0|I|Y|B|3B|K|0|E|4|M|B|0|0|3|I|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|P|$]]

<code>std::unordered_set</code> uses hashes to identify objects uniquely. It computes the hash using <code>std::hash&lt;&gt;</code> structure. This is fine for primitive or STL containers as they have defined a hash structure for them. But for your case, there isn't a hash structure to generate the hash. The error says it: <code>std::__1::hash&lt;coor&gt;</code>.
To resolve this, we need to implement a <code>std::hash&lt;&gt;</code> for <code>coor</code>.
<pre class="lang-cpp prettyprint-override"><code>namespace std {
 template&lt;&gt;
 struct hash&lt;coor&gt; {
 const size_t operator()(const coor&amp; c) const
 {
 return std::hash&lt;int&gt;()(c.x) ^ std::hash&lt;int&gt;()(c.y); 
 }
 };
}
</code></pre>
Now the <code>std::unordered_set</code> has the required hash structure to compute the hash.

blocks|key|3999543|text|许多人使用cppreference中给出的解决方案。请参阅here。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3999544|但它们始终打开std命名空间并专门为std::hash指定模板|style|CODE|3999545|基本上这是没有必要的。|3999546|根据定义为here的std::unordered_set的定义，我们需要一个hash函数和一个equal函数。对于hash函数，我们只需要一个operator()。|3999547|因此，我们可以很容易地将其作为结构的一部分。我们需要重写()-operator并实现散列函数。然后我们需要重写==-operator来获得equal函数。|3999548|然后，我们添加我们的结构名称作为额外的模板参数。|3999549|在我看来，最好将散列和相等函数封装在我们的结构中，因为只有这种数据类型应该知道如何计算值。|3999550|请看这里：|3999551|#include+<unordered_set>
#include+<vector>
#include+<iostream>

struct+coor+{
++++int+x{},+y{};

++++//+Hash+function
++++size_t+operator()(const+coor&+c)+const+{+return+std::hash<int>()(c.x)+%5E+std::hash<int>()(c.y);+}
++++//+Equal+Function
++++bool+operator==(const+coor&+other)+const+{+return+(x+==+other.x+&&+y+==+other.y);+}
++++
};

int+main()+{

++++//+Some+test+values
++++std::vector<coor>+test{+{1,2},+{3,4},+{5,6},+{1,2}+};

++++//+Define+the+unordered+set+anf+fill+it+with+test+value
++++std::unordered_set<coor,+coor>+myset(test.begin(),+test.end());

++++//+Show+result.+There+is+no+double+value+1,2
++++for+(const+coor&+c+:+myset)+std::cout+<<+c.x+<<+'+'+<<+c.y+<<+'\n';

++++return+0;
}|code-block|syntax|javascript|3999552|3999553|当然，您也可以将Lambdas作为散列和相等的“自由”函数。|3999554|在下面的示例中，我们将定义两个Lambdas，一个用于计算散列，另一个用于计算等于函数。|3999555|因为Lambda的类型只有编译器知道，所以我们在模板参数中使用decltype来通知编译器，我们将在模板中使用哪个函数“类型”。|3999556|作为示例，我使用所有5个可用的构造函数定义了变量定义。具体说明请参考here。|3999557|请注意:如果您将operator==添加到如上所示的结构中，则可以随时随地删除"myEqual“函数。|3999558|请参考下面的示例：|3999559|#include+<unordered_set>
#include+<vector>
#include+<iostream>

struct+coor+{
++++int+x{},+y{};
};

constexpr+size_t+BucketCount+=+20u;
int+main()+{
++++//+Hash+function
++++auto+myHash+=+[](const+coor&+c)+{+return+std::hash<int>()(c.x)+%5E+std::hash<int>()(c.y);+};
++++//+Equal+function
++++auto+myEqual+=+[](const+coor&+c1,+const+coor&+c2)+{+return+c1.x+==+c2.x+&&+c1.y+==+c2.y;+};

++++//+Constructor+Number+1
++++std::unordered_set<coor,+decltype(myHash),+decltype(myEqual)>+myset1(BucketCount,+myHash,+myEqual);
++++myset1.insert({+1,2+});+myset1.insert({+3,4+});+myset1.insert({+5,6+});+myset1.insert({+1,2+});

++++//+Constructor+Number+2
++++std::vector<coor>+test{+{1,2},+{3,4},+{5,6},+{1,2}+};//+Some+test+values
++++std::unordered_set<coor,+decltype(myHash),+decltype(myEqual)>+myset2(test.begin(),test.end(),+BucketCount,+myHash,+myEqual);

++++//+Constructor+Number+3
++++std::unordered_set<coor,+decltype(myHash),+decltype(myEqual)>+myset3(myset2);

++++//+Constructor+Number+4
++++std::unordered_set<coor,+decltype(myHash),+decltype(myEqual)>+mysetTemp(myset2);
++++std::unordered_set<coor,+decltype(myHash),+decltype(myEqual)>+myset4(std::move(mysetTemp));

++++//+Constructor+Number+5
++++std::unordered_set<coor,+decltype(myHash),+decltype(myEqual)>+myset5({+{1,2},+{3,4},+{5,6},+{1,2}+},+BucketCount,+myHash,+myEqual);

++++//+Show+result.+There+is+no+double+value+1,2
++++for+(const+coor&+c+:+myset1)+std::cout+<<+c.x+<<+'+'+<<+c.y+<<+'\n';+std::cout+<<+'\n';
++++for+(const+coor&+c+:+myset2)+std::cout+<<+c.x+<<+'+'+<<+c.y+<<+'\n';+std::cout+<<+'\n';
++++for+(const+coor&+c+:+myset3)+std::cout+<<+c.x+<<+'+'+<<+c.y+<<+'\n';+std::cout+<<+'\n';
++++for+(const+coor&+c+:+myset4)+std::cout+<<+c.x+<<+'+'+<<+c.y+<<+'\n';+std::cout+<<+'\n';
++++for+(const+coor&+c+:+myset5)+std::cout+<<+c.x+<<+'+'+<<+c.y+<<+'\n';+std::cout+<<+'\n';
++++return+0;
}|3999560|3999561|使用Microsoft+Visual+Studio+Community+2019版本16.8.2进行开发、编译和测试|3999562|使用gcc10和clang+11进行额外编译和测试|3999563|语言:+C%2B%2B17|3999564|3999565|如果你对上述问题有任何疑问，我很乐意回答。|3999566|entityMap|0|LINK|mutability|MUTABLE|url|https://en.cppreference.com/w/cpp/utility/hash/operator())|1|https://en.cppreference.com/w/cpp/container/unordered_set|2|https://en.cppreference.com/w/cpp/container/unordered_set/unordered_set^0|T|4|0|0|7|3|I|9|0|0|A|I|12|4|1B|5|1L|4|1Z|A|5|4|1|0|S|2|1J|2|0|0|0|0|0|0|0|0|V|8|0|Y|4|2|0|8|A|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1Z|8|@]|9|@$A|20|B|21|1|22]]|C|$]]|$1|D|3|E|5|6|7|23|8|@$A|24|B|25|F|G]|$A|26|B|27|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|28|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|29|8|@$A|2A|B|2B|F|G]|$A|2C|B|2D|F|G]|$A|2E|B|2F|F|G]|$A|2G|B|2H|F|G]|$A|2I|B|2J|F|G]]|9|@$A|2K|B|2L|1|2M]]|C|$]]|$1|L|3|M|5|6|7|2N|8|@$A|2O|B|2P|F|G]|$A|2Q|B|2R|F|G]]|9|@]|C|$]]|$1|N|3|O|5|6|7|2S|8|@]|9|@]|C|$]]|$1|P|3|Q|5|6|7|2T|8|@]|9|@]|C|$]]|$1|R|3|S|5|6|7|2U|8|@]|9|@]|C|$]]|$1|T|3|U|5|V|7|2V|8|@]|9|@]|C|$W|X]]|$1|Y|3|-4|5|6|7|2W|8|@]|9|@]|C|$]]|$1|Z|3|10|5|6|7|2X|8|@]|9|@]|C|$]]|$1|11|3|12|5|6|7|2Y|8|@]|9|@]|C|$]]|$1|13|3|14|5|6|7|2Z|8|@$A|30|B|31|F|G]]|9|@]|C|$]]|$1|15|3|16|5|6|7|32|8|@]|9|@$A|33|B|34|1|35]]|C|$]]|$1|17|3|18|5|6|7|36|8|@$A|37|B|38|F|G]]|9|@]|C|$]]|$1|19|3|1A|5|6|7|39|8|@]|9|@]|C|$]]|$1|1B|3|1C|5|V|7|3A|8|@]|9|@]|C|$W|X]]|$1|1D|3|-4|5|6|7|3B|8|@]|9|@]|C|$]]|$1|1E|3|1F|5|6|7|3C|8|@]|9|@]|C|$]]|$1|1G|3|1H|5|6|7|3D|8|@]|9|@]|C|$]]|$1|1I|3|1J|5|6|7|3E|8|@]|9|@]|C|$]]|$1|1K|3|-4|5|6|7|3F|8|@]|9|@]|C|$]]|$1|1L|3|1M|5|6|7|3G|8|@]|9|@]|C|$]]|$1|1N|3|-4|5|6|7|3H|8|@]|9|@]|C|$]]]|1O|$1P|$5|1Q|1R|1S|C|$1T|1U]]|1V|$5|1Q|1R|1S|C|$1T|1W]]|1X|$5|1Q|1R|1S|C|$1T|1Y]]]]

Many people use the solution given in the cppreference. Please see <a href="https://en.cppreference.com/w/cpp/utility/hash/operator()" rel="nofollow noreferrer">here</a>.
But they always open the <code>std</code> namespace and specialize the template for <code>std::hash</code>
Basically that is not necessary.
According to the definition of the <code>std::unordered_set</code> as defined <a href="https://en.cppreference.com/w/cpp/container/unordered_set" rel="nofollow noreferrer">here</a>, we need a <code>hash</code> function and an <code>equal</code> function. And for the <code>hash</code> function we just need an <code>operator()</code>.
So, we can make this easily as a part of our struct. We need to overide the <code>()</code>-operator and implement the hash function. And then we need to override the <code>==</code>-operator to get the equal function.
Then we add the our struct name as an additional template parameter.
In my humble opinion, it is better to encapsulate the hash and equal functions in our struct, because only this datatype should know, how to calculate values.
Please see here:
<pre><code>#include &lt;unordered_set&gt;
#include &lt;vector&gt;
#include &lt;iostream&gt;

struct coor {
 int x{}, y{};

 // Hash function
 size_t operator()(const coor&amp; c) const { return std::hash&lt;int&gt;()(c.x) ^ std::hash&lt;int&gt;()(c.y); }
 // Equal Function
 bool operator==(const coor&amp; other) const { return (x == other.x &amp;&amp; y == other.y); }
 
};

int main() {

 // Some test values
 std::vector&lt;coor&gt; test{ {1,2}, {3,4}, {5,6}, {1,2} };

 // Define the unordered set anf fill it with test value
 std::unordered_set&lt;coor, coor&gt; myset(test.begin(), test.end());

 // Show result. There is no double value 1,2
 for (const coor&amp; c : myset) std::cout &lt;&lt; c.x &lt;&lt; ' ' &lt;&lt; c.y &lt;&lt; '\n';

 return 0;
}
</code></pre>
<hr />
Of course you may also Lambdas as &quot;free&quot; functions for the hash and the equal.
In the following example, we will define 2 Lambdas, one for calculating the hash and one calculating the equal function.
Since the type of the Lambda is only known to the compiler, we use <code>decltype</code> in the template parameter, to inform the compiler, which function &quot;type&quot; we will use in the template.
As an example I defined variable definitions using all 5 available constructors. Please see <a href="https://en.cppreference.com/w/cpp/container/unordered_set/unordered_set" rel="nofollow noreferrer">here</a> for the description.
Please note: You can always and everywhere delete the &quot;myEqual&quot; function, if you add the <code>operator==</code> to the struct as shown above.
Please see the next example below:
<pre><code>#include &lt;unordered_set&gt;
#include &lt;vector&gt;
#include &lt;iostream&gt;

struct coor {
 int x{}, y{};
};

constexpr size_t BucketCount = 20u;
int main() {
 // Hash function
 auto myHash = [](const coor&amp; c) { return std::hash&lt;int&gt;()(c.x) ^ std::hash&lt;int&gt;()(c.y); };
 // Equal function
 auto myEqual = [](const coor&amp; c1, const coor&amp; c2) { return c1.x == c2.x &amp;&amp; c1.y == c2.y; };

 // Constructor Number 1
 std::unordered_set&lt;coor, decltype(myHash), decltype(myEqual)&gt; myset1(BucketCount, myHash, myEqual);
 myset1.insert({ 1,2 }); myset1.insert({ 3,4 }); myset1.insert({ 5,6 }); myset1.insert({ 1,2 });

 // Constructor Number 2
 std::vector&lt;coor&gt; test{ {1,2}, {3,4}, {5,6}, {1,2} };// Some test values
 std::unordered_set&lt;coor, decltype(myHash), decltype(myEqual)&gt; myset2(test.begin(),test.end(), BucketCount, myHash, myEqual);

 // Constructor Number 3
 std::unordered_set&lt;coor, decltype(myHash), decltype(myEqual)&gt; myset3(myset2);

 // Constructor Number 4
 std::unordered_set&lt;coor, decltype(myHash), decltype(myEqual)&gt; mysetTemp(myset2);
 std::unordered_set&lt;coor, decltype(myHash), decltype(myEqual)&gt; myset4(std::move(mysetTemp));

 // Constructor Number 5
 std::unordered_set&lt;coor, decltype(myHash), decltype(myEqual)&gt; myset5({ {1,2}, {3,4}, {5,6}, {1,2} }, BucketCount, myHash, myEqual);

 // Show result. There is no double value 1,2
 for (const coor&amp; c : myset1) std::cout &lt;&lt; c.x &lt;&lt; ' ' &lt;&lt; c.y &lt;&lt; '\n'; std::cout &lt;&lt; '\n';
 for (const coor&amp; c : myset2) std::cout &lt;&lt; c.x &lt;&lt; ' ' &lt;&lt; c.y &lt;&lt; '\n'; std::cout &lt;&lt; '\n';
 for (const coor&amp; c : myset3) std::cout &lt;&lt; c.x &lt;&lt; ' ' &lt;&lt; c.y &lt;&lt; '\n'; std::cout &lt;&lt; '\n';
 for (const coor&amp; c : myset4) std::cout &lt;&lt; c.x &lt;&lt; ' ' &lt;&lt; c.y &lt;&lt; '\n'; std::cout &lt;&lt; '\n';
 for (const coor&amp; c : myset5) std::cout &lt;&lt; c.x &lt;&lt; ' ' &lt;&lt; c.y &lt;&lt; '\n'; std::cout &lt;&lt; '\n';
 return 0;
}
</code></pre>
<hr />
Developed compiled and tested with Microsoft Visual Studio Community 2019, Version 16.8.2
Additionally compiled and tested with gcc10 amnd clang 11
Language: C++17
<hr />
If you have any questions to the above, then I am happy to answer

I have been trying to make an unordered_set of structs in c++ but it seems to give me this error-
<pre><code>error: call to implicitly-deleted default constructor
 of 'std::__1::hash&lt;coor&gt;'
 __compressed_pair_elem(__default_init_tag) {}
</code></pre>
I included a == operator, can assist me in making a unordered_set of structures?
<pre><code>#include &lt;iostream&gt;
#include &lt;vector&gt;
#include &lt;unordered_set&gt;
#include &lt;algorithm&gt;
using namespace std;
struct coor{
 int x,y;
 bool operator==(coor a) const{
 if(a.x == x &amp;&amp; a.y == y){
 return true;
 }
 else return false;
 };
};
int main(){
 unordered_set&lt;coor&gt; myset;
}
</code></pre>

An unordered set of structs

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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我一直试图在c++中创建一个结构的unordered_set，但它似乎给了我这个错误-error: call to implicitly-deleted default constructor of 'std::__1::hash<coor>' __compressed_pair_elem(__defaul...

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