[英]Moving an std::unordered_map values to std::vector
Is there any way to move unordered_map
values to a vector? 有没有办法将
unordered_map
值移动到向量? All the ways I was able to find copy values (like in my example) instead of using something similar to std::move
. 我能够找到复制值的所有方法(比如我的例子),而不是使用类似于
std::move
东西。
I would like to not copy values so I can retain uniqueness of shared_ptr
foo, which I'll later change to unique_ptr
. 我想不复制值,所以我可以保留
shared_ptr
foo的唯一性,我稍后会更改为unique_ptr
。
class Class {
public:
std::shared_ptr <int> foo = std::shared_ptr <int> (new int (5));
};
int main() {
std::unordered_map <int, Class> mapOfObjects({
{1, Class()},
{2, Class()},
{3, Class()},
{4, Class()},
{5, Class()} });
std::vector <Class> someVector;
for (auto &object : mapOfObjects) {
someVector.push_back(object.second);
std::cout << "Is unique? " << ( someVector.back().foo.unique() ? "Yes." : "No.")
<< std::endl << std::endl;
}
}
Thank you in advance for all helpful answers. 提前感谢您提供所有有用的答案。
You can certainly move shared_ptr
from unordered_map
to vector
. 你当然可以将
shared_ptr
从unordered_map
移动到vector
。 All you need to do is to use std::move
in your example: 您需要做的就是在您的示例中使用
std::move
:
someVector.push_back(std::move(object.second));
Keep in mind, after this operation, you might want to clear the map, as it now contains empty objects. 请记住,在此操作之后,您可能希望清除地图,因为它现在包含空对象。
@SergeyA's answer already covers the essential part here, let me nevertheless add a solution based on range-v3 , it shows where one part of the language is heading to with C++20. @ SergeyA的答案已经涵盖了这里的基本部分,但是我还是添加了一个基于range-v3的解决方案,它显示了C ++ 20中语言的一部分。
#include <range/v3/view/map.hpp>
#include <range/v3/view/move.hpp>
using namespace ranges;
/* Setup mapOfObjects... */
const std::vector<Class> someVector = mapOfObjects | view::values | view::move;
The STL in its current shape isn't that bad either, but admittetly more verbose: 目前形状的STL也不是那么糟糕,但是更加冗长:
#include <algorithm>
#include <iterator>
std::vector<Class> someVector;
std::transform(std::move_iterator(mapOfObjects.begin()),
std::move_iterator(mapOfObjects.end()),
std::back_inserter(someVector),
[](std::pair<int, Class>&& entry){ return std::move(entry.second); });
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