blocks|key|576365|text|是：std::for_each。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|576366|#include+<algorithm>+//std::for_each

void+foo(int+a)+{
++++std::cout+<<+a+<<+"\n";
}

std::vector<int>+v;

...

std::for_each(v.begin(),+v.end(),+&foo);|code-block|syntax|javascript|576367|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/algorithm/for_each^0|2|D|2|D|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

Yes: <a href="http://en.cppreference.com/w/cpp/algorithm/for_each" rel="noreferrer"><code>std::for_each</code></a>.

<pre><code>#include &lt;algorithm&gt; //std::for_each

void foo(int a) {
 std::cout &lt;&lt; a &lt;&lt; "\n";
}

std::vector&lt;int&gt; v;

...

std::for_each(v.begin(), v.end(), &amp;foo);
</code></pre>

blocks|key|360747|text|在C%2B%2B+11上:您可以使用lambda。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|360748|std::vector<int>+nums{3,+4,+2,+9,+15,+267};

std::for_each(nums.begin(),+nums.end(),+[](int+&n){+n%2B%2B;+});|code-block|syntax|javascript|360749|参考：http://en.cppreference.com/w/cpp/algorithm/for_each|offset|length|360750|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/algorithm/for_each^0|0|0|3|1F|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

On C++ 11: You could use a lambda. For example:

<pre><code>std::vector&lt;int&gt; nums{3, 4, 2, 9, 15, 267};

std::for_each(nums.begin(), nums.end(), [](int &amp;n){ n++; });
</code></pre>

ref: <a href="http://en.cppreference.com/w/cpp/algorithm/for_each" rel="noreferrer">http://en.cppreference.com/w/cpp/algorithm/for_each</a>

blocks|key|360696|text|如果你有C%2B%2B11，还有一个更短的方法：ranged-based+for。它的目的就是这样。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|360697|std::vector<int>+v+{1,2,3,4,5};

for+(int+element+:+v)
++++std::cout+<<+element;+//prints+12345|code-block|syntax|javascript|360698|您还可以在适当的时候对其应用引用和const，或者在类型为long时使用auto。|360699|std::vector<std::vector<int>>+v+{{1,2,3},{4,5,6}};

for+(const+auto+&vec+:+v)
{
++++for+(int+element+:+vec)
++++++++cout+<<+element;

++++cout+<<+'\n';
}+|360700|输出：|360701|123
456|360702|entityMap|0|LINK|mutability|MUTABLE|url|http://www2.research.att.com/~bs/C%2B%2B0xFAQ.html#for^0|K|G|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|R|$S|$5|T|U|V|C|$W|X]]]]

If you have C++11, there's an even shorter method: <a href="http://www2.research.att.com/~bs/C++0xFAQ.html#for" rel="noreferrer">ranged-based for</a>. Its purpose is exactly this.

<pre><code>std::vector&lt;int&gt; v {1,2,3,4,5};

for (int element : v)
 std::cout &lt;&lt; element; //prints 12345
</code></pre>

You can also apply references and const to it as well, when appropriate, or use auto when the type is long.

<pre><code>std::vector&lt;std::vector&lt;int&gt;&gt; v {{1,2,3},{4,5,6}};

for (const auto &amp;vec : v)
{
 for (int element : vec)
 cout &lt;&lt; element;

 cout &lt;&lt; '\n';
} 
</code></pre>

Output:

<pre><code>123
456
</code></pre>

blocks|key|576415|text|使用for_each|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|576416|//+for_each+example
#include+<iostream>
#include+<algorithm>
#include+<vector>
using+namespace+std;

void+myfunction+(int+i)+{
++cout+<<+"+"+<<+i;
}

struct+myclass+{
++void+operator()+(int+i)+{cout+<<+"+"+<<+i;}
}+myobject;

int+main+()+{
++vector<int>+myvector;
++myvector.push_back(10);
++myvector.push_back(20);
++myvector.push_back(30);

++cout+<<+"myvector+contains:";
++for_each+(myvector.begin(),+myvector.end(),+myfunction);

++//+or:
++cout+<<+"\nmyvector+contains:";
++for_each+(myvector.begin(),+myvector.end(),+myobject);

++cout+<<+endl;

++return+0;
}|code-block|syntax|javascript|576417|entityMap^0|2|8|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|$]]

Use <code>for_each</code>:

<pre><code>// for_each example
#include &lt;iostream&gt;
#include &lt;algorithm&gt;
#include &lt;vector&gt;
using namespace std;

void myfunction (int i) {
 cout &lt;&lt; " " &lt;&lt; i;
}

struct myclass {
 void operator() (int i) {cout &lt;&lt; " " &lt;&lt; i;}
} myobject;

int main () {
 vector&lt;int&gt; myvector;
 myvector.push_back(10);
 myvector.push_back(20);
 myvector.push_back(30);

 cout &lt;&lt; "myvector contains:";
 for_each (myvector.begin(), myvector.end(), myfunction);

 // or:
 cout &lt;&lt; "\nmyvector contains:";
 for_each (myvector.begin(), myvector.end(), myobject);

 cout &lt;&lt; endl;

 return 0;
}
</code></pre>

blocks|key|576606|text|这个OP提到了Python中的map函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|576607|这个Python函数实际上将一个函数应用于列表(或可迭代)的每个元素，并返回一个收集所有结果的列表(或可迭代)。|576608|换句话说，它是这样做的：|576609|def+f(+x+)+:+
+++"""+a+function+that+computes+something+with+x"""
+++#+code+here+
+++return+y+

input+=+[+x1,+x2,+x3,+...+]
output+=+map(+func,+input+)++

#+output+is++now+[+f(x1),+f(x2),+f(x3),+...]+|code-block|syntax|javascript|576610|因此，与Python最接近的C%2B%2B标准库实际上是std::transform+(来自<algorithm>标头)。|576611|示例用法如下：|576612|#include+<vector>
#include+<algorithm>+
using+namespace+std;

double+f(+int+x+)+{+
+++//+a+function+that+computes+the+square+of+x+divided+by+2.0+
+++return+x+*+x+/+2.0+;
}

int+main(+)+{
++vector<int>+input{+1,+5,+10+,+20};
++vector<double>+output;
++output.resize(+input.size()+);+//+unfortunately+this+is+necessary

++std::transform(+input.begin(),+input.end(),+output.begin(),+f+);

++//+output+now+contains++{+f(1),+f(5),+f(10),+f(20)+}
++//+++++++++++++++++++++=+{+0.5,+12.5,++50.0,+200.0+}+
++return+0;
}+++|576613|entityMap|0|LINK|mutability|MUTABLE|url|https://thepythonguru.com/python-builtin-functions/map/|1|http://www.cplusplus.com/reference/algorithm/transform/^0|F|3|F|3|0|0|0|0|0|O|E|16|B|O|E|1|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1B|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1C|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@$9|1I|A|1J|1|1K]]|E|$]]|$1|Q|3|R|5|6|7|1L|8|@]|D|@]|E|$]]|$1|S|3|T|5|L|7|1M|8|@]|D|@]|E|$M|N]]|$1|U|3|-4|5|6|7|1N|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]|12|$5|X|Y|Z|E|$10|13]]]]

The OP mentions the <a href="https://thepythonguru.com/python-builtin-functions/map/" rel="nofollow noreferrer"><code>map</code></a> function in Python.
This Python function actually applies a function to every element of a list (or iterable) and returns a list (or iterable) that collects all results.
In other words, it does something like this:
<pre class="lang-py prettyprint-override"><code>def f( x ) : 
 &quot;&quot;&quot; a function that computes something with x&quot;&quot;&quot;
 # code here 
 return y 

input = [ x1, x2, x3, ... ]
output = map( func, input ) 

# output is now [ f(x1), f(x2), f(x3), ...] 
</code></pre>
Hence, the closest C++ standard-library equivalent to Python's map is actually <a href="http://www.cplusplus.com/reference/algorithm/transform/" rel="nofollow noreferrer"><code>std::transform</code></a> (from the <code>&lt;algorithm&gt;</code> header).
Example usage is as follows:
<pre class="lang-c++ prettyprint-override"><code>#include &lt;vector&gt;
#include &lt;algorithm&gt; 
using namespace std;

double f( int x ) { 
 // a function that computes the square of x divided by 2.0 
 return x * x / 2.0 ;
}

int main( ) {
 vector&lt;int&gt; input{ 1, 5, 10 , 20};
 vector&lt;double&gt; output;
 output.resize( input.size() ); // unfortunately this is necessary

 std::transform( input.begin(), input.end(), output.begin(), f );

 // output now contains { f(1), f(5), f(10), f(20) }
 // = { 0.5, 12.5, 50.0, 200.0 } 
 return 0;
} 
</code></pre>

blocks|key|360621|text|您可以使用std::for_each，它接受一对迭代器和一个函数或函数器。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|360622|entityMap|0|LINK|mutability|MUTABLE|url|http://en.cppreference.com/w/cpp/algorithm/for_each^0|5|D|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can use <a href="http://en.cppreference.com/w/cpp/algorithm/for_each" rel="nofollow">std::for_each</a> which takes a pair of iterators and a function or functor.

blocks|key|576662|text|我想我会分享for_each和transform的std::ranges等效物，如果有人喜欢它们的话：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|576663|std::vector<int>+v;

std::ranges::for_each(v,[](const+auto&+n)+{});

const+auto+squared+=+v+%7C+std::views::transform([](const+auto&+n)+{+return+n*2;+});|code-block|syntax|javascript|576664|在龙箭上运行：https://godbolt.org/z/zYME6b|576665|entityMap|0|LINK|mutability|MUTABLE|url|https://godbolt.org/z/zYME6b^0|6|8|F|9|P|B|0|0|7|S|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@$9|13|A|14|1|15]]|E|$]]|$1|M|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Thought I would share <code>std::ranges</code> equivalents for <code>for_each</code> and <code>transform</code>, should anyone prefer them:
<pre><code>std::vector&lt;int&gt; v;

std::ranges::for_each(v,[](const auto&amp; n) {});

const auto squared = v | std::views::transform([](const auto&amp; n) { return n*2; });
</code></pre>
Running on godbolt: <a href="https://godbolt.org/z/zYME6b" rel="nofollow noreferrer">https://godbolt.org/z/zYME6b</a>

In C++, is there a way to call a function on each element of a vector, without using a loop running over all vector elements? Something similar to a 'map' in Python.

Calling a function on every element of a C++ vector

Python

在C++中，有没有一种方法可以在向量的每个元素上调用函数，而不使用遍历所有向量元素的循环？类似于Python中的“map”。

问在C++向量的每个元素上调用函数
EN

回答 7

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