entityMap|blocks|key|fkc29|text|AB.reserve(+A.size()+%2B+B.size()+);+//+preallocate+memory
AB.insert(+AB.end(),+A.begin(),+A.end()+);
AB.insert(+AB.end(),+B.begin(),+B.end()+);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>AB.reserve( A.size() + B.size() ); // preallocate memory
AB.insert( AB.end(), A.begin(), A.end() );
AB.insert( AB.end(), B.begin(), B.end() );
</code></pre>

entityMap|blocks|key|62to6|text|这正是成员函数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|8gccn|是为了|5jeb4|std::vector+AB+=+A;
AB.insert(AB.end(),+B.begin(),+B.end());|code-block|syntax|javascript^0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|J|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|K|9|@]|A|@]|B|$]]|$2|E|4|F|6|G|8|L|9|@]|A|@]|B|$H|I]]]]

This is precisely what the member function <code>std::vector::insert</code> is for

<pre><code>std::vector&lt;int&gt; AB = A;
AB.insert(AB.end(), B.begin(), B.end());
</code></pre>

entityMap|blocks|key|apc3u|text|这取决于您是否真的需要在物理上连接这两个向量，或者您是否希望为了迭代而提供连接的外观。boost::join函数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|r9hn|http://www.boost.org/doc/libs/1|5rs6k|_|3rjb8|43|d3jna|69ge4|0/libs/range/doc/html/range/reference/utilities/join.html|f6hru|会给你这个。|1vb66|std::vector+v0;
v0.push_back(1);
v0.push_back(2);
v0.push_back(3);

std::vector+v1;
v1.push_back(4);
v1.push_back(5);
v1.push_back(6);
...

BOOST_FOREACH(const+int+&+i,+boost::join(v0,+v1)){
++++cout+<<+i+<<+endl;
}|code-block|syntax|javascript|adbml|应该会给你|6kda2|1
2
3
4
5
6|iuct|注boost::join不会将这两个向量复制到新的容器中，但会生成一对迭代器(范围)，覆盖两个容器的跨度。会有一些性能开销，但可能会减少首先将所有数据复制到新容器的开销。^0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|Y|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|Z|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|10|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|11|9|@]|A|@]|B|$]]|$2|I|4|F|6|7|8|12|9|@]|A|@]|B|$]]|$2|J|4|K|6|7|8|13|9|@]|A|@]|B|$]]|$2|L|4|M|6|7|8|14|9|@]|A|@]|B|$]]|$2|N|4|O|6|P|8|15|9|@]|A|@]|B|$Q|R]]|$2|S|4|T|6|7|8|16|9|@]|A|@]|B|$]]|$2|U|4|V|6|P|8|17|9|@]|A|@]|B|$Q|R]]|$2|W|4|X|6|7|8|18|9|@]|A|@]|B|$]]]]

Depends on whether you really need to physically concatenate the two vectors or you want to give the appearance of concatenation of the sake of iteration. The boost::join function

<a href="http://www.boost.org/doc/libs/1_43_0/libs/range/doc/html/range/reference/utilities/join.html" rel="noreferrer">http://www.boost.org/doc/libs/1_43_0/libs/range/doc/html/range/reference/utilities/join.html</a>

will give you this.

<pre><code>std::vector&lt;int&gt; v0;
v0.push_back(1);
v0.push_back(2);
v0.push_back(3);

std::vector&lt;int&gt; v1;
v1.push_back(4);
v1.push_back(5);
v1.push_back(6);
...

BOOST_FOREACH(const int &amp; i, boost::join(v0, v1)){
 cout &lt;&lt; i &lt;&lt; endl;
}
</code></pre>

should give you 

<pre><code>1
2
3
4
5
6
</code></pre>

Note boost::join does not copy the two vectors into a new container
but generates a pair of iterators (range) that cover the span of
both containers. There will be some performance overhead but maybe
less that copying all the data to a new container first.

entityMap|blocks|key|28l06|text|基于|type|unstyled|depth|inlineStyleRanges|entityRanges|data|c89vl|Kiril+V.+Lyadvinsky回答|53l5l|，我做了一个新版本。此代码段使用模板和重载。使用它，您可以编写|8garr|和|9aj64|..。希望能有所帮助。|di5n3|template+
std::vector+operator%2B(const+std::vector+&A,+const+std::vector+&B)
{
++++std::vector+AB;
++++AB.reserve(A.size()+%2B+B.size());++++++++++++++++//+preallocate+memory
++++AB.insert(AB.end(),+A.begin(),+A.end());++++++++//+add+A;
++++AB.insert(AB.end(),+B.begin(),+B.end());++++++++//+add+B;
++++return+AB;
}

template+
std::vector+&operator%2B=(std::vector+&A,+const+std::vector+&B)
{
++++A.reserve(A.size()+%2B+B.size());++++++++++++++++//+preallocate+memory+without+erase+original+data
++++A.insert(A.end(),+B.begin(),+B.end());+++++++++//+add+B;
++++return+A;++++++++++++++++++++++++++++++++++++++++//+here+A+could+be+named+AB
}|code-block|syntax|javascript^0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|P|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|Q|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|R|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|S|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|T|9|@]|A|@]|B|$]]|$2|K|4|L|6|M|8|U|9|@]|A|@]|B|$N|O]]]]

Based on <a href="https://stackoverflow.com/a/3177252/1248177">Kiril V. Lyadvinsky answer</a>, I made a new version. This snippet use template and overloading. With it, you can write <code>vector3 = vector1 + vector2</code> and <code>vector4 += vector3</code>. Hope it can help.

<pre><code>template &lt;typename T&gt;
std::vector&lt;T&gt; operator+(const std::vector&lt;T&gt; &amp;A, const std::vector&lt;T&gt; &amp;B)
{
 std::vector&lt;T&gt; AB;
 AB.reserve(A.size() + B.size()); // preallocate memory
 AB.insert(AB.end(), A.begin(), A.end()); // add A;
 AB.insert(AB.end(), B.begin(), B.end()); // add B;
 return AB;
}

template &lt;typename T&gt;
std::vector&lt;T&gt; &amp;operator+=(std::vector&lt;T&gt; &amp;A, const std::vector&lt;T&gt; &amp;B)
{
 A.reserve(A.size() + B.size()); // preallocate memory without erase original data
 A.insert(A.end(), B.begin(), B.end()); // add B;
 return A; // here A could be named AB
}
</code></pre>

entityMap|blocks|key|3q5cn|text|在Bradgonesurfing的答案中，很多时候人们并不是真的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|f1cs7|需求|m2np|连接两个向量(O(n))，而不是|878v7|像连接在一起一样使用它们(O(1))|50a0k|..。如果这是您的情况，则可以在不需要Boost库的情况下完成。|5ol4n|诀窍是创建一个向量代理:一个包装类，它操作|6i4i0|参考文献|eje0b|到这两个向量，从外部看是一个连续的向量。|ebbf0|用法|dktsl|std::vector+A{+1,+2,+3,+4,+5};
std::vector+B{+10,+20,+30+};

VecProxy+AB(A,+B);++//+---->+O(1).+No+copies+performed.

for+(size_t+i+=+0;+i+<+AB.size();+%2B%2Bi)
++++std::cout+<<+AB[i]+<<+"+";++//+1+2+3+4+5+10+20+30|code-block|syntax|javascript|728dg|实现|2n9qi|template+
class+VecProxy+{
private:
++++std::vector&+v1,+v2;
public:
++++VecProxy(std::vector&+ref1,+std::vector&+ref2)+:+v1(ref1),+v2(ref2)+{}
++++const+T&+operator[](const+size_t&+i)+const;
++++const+size_t+size()+const;
};

template+
const+T&+VecProxy::operator[](const+size_t&+i)+const{
++++return+(i+<+v1.size())+?+v1[i]+:+v2[i+-+v1.size()];
};

template+
const+size_t+VecProxy::size()+const+{+return+v1.size()+%2B+v2.size();+};|lmcd|主要优势|fbe0|创建它的时间是O(1)+(常数时间)，并且只需要最少的额外内存分配。|ddgjs|一些需要考虑的事情|b2nmq|只有当你在处理引用时真正知道你在做什么的时候，你才应该去尝试它|e58ll|..。|9mhuu|这个解决方案是为所提出的问题的特定目的而设计的，对于这个问题，它工作得很好。|c19h9|..。如果您不确定引用是如何工作的，那么在任何其他上下文中使用它都可能导致意外的行为。|fltus|在此示例中，AB执行以下操作|t772|注释|5pne6|提供非常数访问运算符(|3pmko|669gt|)。可以随意包含它，但请记住:由于AB包含引用，为它赋值也会影响A和/或B中的原始元素。无论这是不是一个理想的特性，这是一个应用程序特定的问题，人们应该仔细考虑。|fkv1a|直接对A或B进行的任何更改(如赋值、排序等)也将“修改”AB。这不一定是不好的(实际上，它可能非常方便:+AB不需要显式更新以保持自身与A和B的同步)，但这肯定是一个必须意识到的行为。重要的例外:将A和/或B的大小调整为某物|6p976|更大|50cm5|可能导致这些在内存中重新分配(为了连续空间的需要)，这将反过来使AB无效。|dn4ov|因为每次访问元素之前都有一个测试(即"i+<+v1.size()")，所以VecProxy访问时间虽然不变，但也比向量的访问时间慢一点。|14oe3|这种方法可以推广到n个向量。我还没试过，但这不应该是什么大问题。^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|1Y|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|1Z|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|20|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|21|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|22|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|23|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|24|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|25|9|@]|A|@]|B|$]]|$2|Q|4|R|6|7|8|26|9|@]|A|@]|B|$]]|$2|S|4|T|6|U|8|27|9|@]|A|@]|B|$V|W]]|$2|X|4|Y|6|7|8|28|9|@]|A|@]|B|$]]|$2|Z|4|10|6|U|8|29|9|@]|A|@]|B|$V|W]]|$2|11|4|12|6|7|8|2A|9|@]|A|@]|B|$]]|$2|13|4|14|6|7|8|2B|9|@]|A|@]|B|$]]|$2|15|4|16|6|7|8|2C|9|@]|A|@]|B|$]]|$2|17|4|18|6|7|8|2D|9|@]|A|@]|B|$]]|$2|19|4|1A|6|7|8|2E|9|@]|A|@]|B|$]]|$2|1B|4|1C|6|7|8|2F|9|@]|A|@]|B|$]]|$2|1D|4|1E|6|7|8|2G|9|@]|A|@]|B|$]]|$2|1F|4|1G|6|7|8|2H|9|@]|A|@]|B|$]]|$2|1H|4|1I|6|7|8|2I|9|@]|A|@]|B|$]]|$2|1J|4|1K|6|7|8|2J|9|@]|A|@]|B|$]]|$2|1L|4|-4|6|7|8|2K|9|@]|A|@]|B|$]]|$2|1M|4|1N|6|7|8|2L|9|@]|A|@]|B|$]]|$2|1O|4|1P|6|7|8|2M|9|@]|A|@]|B|$]]|$2|1Q|4|1R|6|7|8|2N|9|@]|A|@]|B|$]]|$2|1S|4|1T|6|7|8|2O|9|@]|A|@]|B|$]]|$2|1U|4|1V|6|7|8|2P|9|@]|A|@]|B|$]]|$2|1W|4|1X|6|7|8|2Q|9|@]|A|@]|B|$]]]]

In the direction of Bradgonesurfing's answer, many times one doesn't really need to concatenate two vectors (O(n)), but instead just work with them as if they were concatenated (O(1)). If this is your case, it can be done without the need of Boost libraries.

The trick is to create a vector proxy: a wrapper class which manipulates references to both vectors, externally seen as a single, contiguous one. 

USAGE

<pre><code>std::vector&lt;int&gt; A{ 1, 2, 3, 4, 5};
std::vector&lt;int&gt; B{ 10, 20, 30 };

VecProxy&lt;int&gt; AB(A, B); // ----&gt; O(1). No copies performed.

for (size_t i = 0; i &lt; AB.size(); ++i)
 std::cout &lt;&lt; AB[i] &lt;&lt; " "; // 1 2 3 4 5 10 20 30
</code></pre>

IMPLEMENTATION

<pre><code>template &lt;class T&gt;
class VecProxy {
private:
 std::vector&lt;T&gt;&amp; v1, v2;
public:
 VecProxy(std::vector&lt;T&gt;&amp; ref1, std::vector&lt;T&gt;&amp; ref2) : v1(ref1), v2(ref2) {}
 const T&amp; operator[](const size_t&amp; i) const;
 const size_t size() const;
};

template &lt;class T&gt;
const T&amp; VecProxy&lt;T&gt;::operator[](const size_t&amp; i) const{
 return (i &lt; v1.size()) ? v1[i] : v2[i - v1.size()];
};

template &lt;class T&gt;
const size_t VecProxy&lt;T&gt;::size() const { return v1.size() + v2.size(); };
</code></pre>

MAIN BENEFIT

It's O(1) (constant time) to create it, and with minimal extra memory allocation. 

SOME STUFF TO CONSIDER

<ul>
<li>You should only go for it if you really know what you're doing when dealing with references. This solution is intended for the specific purpose of the question made, for which it works pretty well. To employ it in any other context may lead to unexpected behavior if you are not sure on how references work.</li>
<li>In this example, AB does not provide a non-const
access operator ([ ]). Feel free to include it, but keep in mind: since AB contains references, to assign it
values will also affect the original elements within A and/or B. Whether or not this is a
desirable feature, it's an application-specific question one should
carefully consider.</li>
<li>Any changes directly made to either A or B (like assigning values,
sorting, etc.) will also "modify" AB. This is not necessarily bad
(actually, it can be very handy: AB does never need to be explicitly
updated to keep itself synchronized to both A and B), but it's
certainly a behavior one must be aware of. Important exception: to resize A and/or B to sth bigger may lead these to be reallocated in memory (for the need of contiguous space), and this would in turn invalidate AB.</li>
<li>Because every access to an element is preceded by a test (namely, "i
&lt; v1.size()"), VecProxy access time, although constant, is also
a bit slower than that of vectors.</li>
<li>This approach can be generalized to n vectors. I haven't tried, but
it shouldn't be a big deal.</li>
</ul>

entityMap|blocks|key|38d7g|text|还有一个还没有被提及的简单变体：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5pmhb|copy(A.begin(),A.end(),std::back_inserter(AB));
copy(B.begin(),B.end(),std::back_inserter(AB));|code-block|syntax|javascript|bvlk9|并使用合并算法：|64bsa|​|834mm|#include+
#include+
#include+
#include+
#include+
#include+

template+class+Container,+class+T>
std::string+toString(const+Container&+v)
{
++++std::stringstream+ss;
++++std::copy(v.begin(),+v.end(),+std::ostream_iterator(ss,+""));
++++return+ss.str();
};


int+main()
{
++++std::vector+A(10);
++++std::vector+B(5);++//zero+filled
++++std::vector+AB(15);

++++std::for_each(A.begin(),+A.end(),
++++++++++++[](int&+f)->void
++++++++++++{
++++++++++++++++f+=+rand()+%25+100;
++++++++++++});

++++std::cout+<<+"before+merge:+"+<<+toString(A)+<<+"\n";
++++std::cout+<<+"before+merge:+"+<<+toString(B)+<<+"\n";
++++merge(B.begin(),B.end(),+begin(A),+end(A),+AB.begin(),+[](int&,int&)->bool+{});
++++std::cout+<<+"after+merge:++"+<<+toString(AB)+<<+"\n";

++++return+1;
}|2go10^0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|O|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|P|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|Q|9|@]|A|@]|B|$]]|$2|J|4|K|6|7|8|R|9|@]|A|@]|B|$]]|$2|L|4|M|6|E|8|S|9|@]|A|@]|B|$F|G]]|$2|N|4|K|6|7|8|T|9|@]|A|@]|B|$]]]]

One more simple variant which was not yet mentioned:

<pre><code>copy(A.begin(),A.end(),std::back_inserter(AB));
copy(B.begin(),B.end(),std::back_inserter(AB));
</code></pre>

And using merge algorithm:

<pre>

<code>#include &lt;algorithm&gt;
#include &lt;vector&gt;
#include &lt;iterator&gt;
#include &lt;iostream&gt;
#include &lt;sstream&gt;
#include &lt;string&gt;

template&lt;template&lt;typename, typename...&gt; class Container, class T&gt;
std::string toString(const Container&lt;T&gt;&amp; v)
{
 std::stringstream ss;
 std::copy(v.begin(), v.end(), std::ostream_iterator&lt;T&gt;(ss, ""));
 return ss.str();
};


int main()
{
 std::vector&lt;int&gt; A(10);
 std::vector&lt;int&gt; B(5); //zero filled
 std::vector&lt;int&gt; AB(15);

 std::for_each(A.begin(), A.end(),
 [](int&amp; f)-&gt;void
 {
 f = rand() % 100;
 });

 std::cout &lt;&lt; "before merge: " &lt;&lt; toString(A) &lt;&lt; "\n";
 std::cout &lt;&lt; "before merge: " &lt;&lt; toString(B) &lt;&lt; "\n";
 merge(B.begin(),B.end(), begin(A), end(A), AB.begin(), [](int&amp;,int&amp;)-&gt;bool {});
 std::cout &lt;&lt; "after merge: " &lt;&lt; toString(AB) &lt;&lt; "\n";

 return 1;
}
</code></pre>

entityMap|blocks|key|8njb1|text|如果您的向量已排序|type|unstyled|depth|inlineStyleRanges|entityRanges|data|7tc3m|*|6call|，查看|586u4|设置|qtmm|_|a9b1t|联合|121t3|从。|5vmrl|set_union(A.begin(),+A.end(),+B.begin(),+B.end(),+AB.begin());|code-block|syntax|javascript|3jvln|在链接中有一个更详细的例子。^0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|V|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|W|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|X|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|Y|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|Z|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|10|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|11|9|@]|A|@]|B|$]]|$2|O|4|P|6|Q|8|12|9|@]|A|@]|B|$R|S]]|$2|T|4|U|6|7|8|13|9|@]|A|@]|B|$]]]]

If your vectors are sorted*, check out <a href="https://www.cplusplus.com/reference/algorithm/set_union/" rel="nofollow noreferrer">set_union</a> from <code>&lt;algorithm&gt;</code>.
<pre><code>set_union(A.begin(), A.end(), B.begin(), B.end(), AB.begin());
</code></pre>
There's a more thorough example in the link.

entityMap|blocks|key|eajmn|text|所有的解决方案都是正确的，但我发现只需编写一个函数来实现它就更容易了。如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3f2pj|template+
void+ContainerInsert(T1+t1,+T2+t2)
{
++++t1->insert(t1->end(),+t2->begin(),+t2->end());
}|code-block|syntax|javascript|5gtih|这样就可以避免像这样的临时放置：|d696o|ContainerInsert(vec,+GetSomeVector());^0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|L|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|M|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|N|9|@]|A|@]|B|$]]|$2|J|4|K|6|E|8|O|9|@]|A|@]|B|$F|G]]]]

All the solutions are correct, but I found it easier just write a function to implement this. like this:

<pre><code>template &lt;class T1, class T2&gt;
void ContainerInsert(T1 t1, T2 t2)
{
 t1-&gt;insert(t1-&gt;end(), t2-&gt;begin(), t2-&gt;end());
}
</code></pre>

That way you can avoid the temporary placement like this:

<pre><code>ContainerInsert(vec, GetSomeVector());
</code></pre>

I'm using multitreading and want to merge the results. For example:

<pre><code>std::vector&lt;int&gt; A;
std::vector&lt;int&gt; B;
std::vector&lt;int&gt; AB;
</code></pre>

I want AB to have to contents of A and the contents of B in that order. What's the most efficient way of doing something like this?

What is the best way to concatenate two vectors?

容器

 我正在使用多路访问，并希望合并结果。例如： std::vector A;std::vector B;std::vector AB; 我想让AB按照A的内容和B的内容的顺序。做这样的事情最有效的方法是什么？

问连接两个向量的最佳方法是什么？
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问连接两个向量的最佳方法是什么？EN

回答 8

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问连接两个向量的最佳方法是什么？
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