[英]Copying one vector into another starting at some position
Say I have two vectors假设我有两个向量
auto a = std::vector<int>{10, 11, 12, 13, 14, 15};
auto b = std::vector<int>{21, 22, 23};
and I want to copy the entire content of b
into a
starting at some position (let's say 4
), possibly overriding elements and resizing the vector, so that the resulting vector a
looks like我想将
b
的全部内容复制到a
中,从 position 开始(假设为4
),可能会覆盖元素并调整向量的大小,以便生成的向量a
看起来像
[10, 11, 12, 13, 21, 22, 23]
Is there some function in the STL (maybe in <algorithm>
or `) that does exactly that? STL 中是否有一些 function(可能在
<algorithm>
或`)中确实如此?
With the help of C++20 <ranges>
借助 C++20
<ranges>
auto a = std::vector{10, 11, 12, 13, 14, 15};
auto b = std::vector{21, 22, 23};
auto pos = 4;
auto c = a | std::views::drop(pos);
auto sz = c.size();
std::ranges::copy(b | std::views::take(sz), c.begin());
std::ranges::copy(b | std::views::drop(sz), std::back_inserter(a));
You can do it like this:你可以这样做:
auto a = std::vector<int>{ 10, 11, 12, 13, 14, 15 };
auto b = std::vector<int>{ 21, 22, 23 };
int from = 4; //from which index
a.insert(a.begin() + from, b.begin(), b.end());
a.resize(from + b.size());
for (auto i : a) {
std::cout << i << " ";
}
There's no ready-made algorithm to do it.没有现成的算法可以做到这一点。 You can implement it yourself like this:
您可以像这样自己实现它:
auto a = std::vector<int>{10, 11, 12, 13, 14, 15};
auto b = std::vector<int>{21, 22, 23};
std::size_t insertionPoint = 4;
std::size_t elemCount = std::max(insertionPoint + b.size(), a.size());
a.resize(elemCount);
std::copy(std::cbegin(b), std::cend(b), std::begin(a) + insertionPoint);
Note:笔记:
std::vector
(ie, in this case, int
) to be default constructible.std::vector
的值类型(即,在本例中为int
)是默认可构造的。insertionPoint
is greater than a.size()
you'll get default constructed elements between the last element of a
(before the insertion) and the first inserted element from b
.insertionPoint
大于a.size()
,您将在a
的最后一个元素(插入之前)和b
的第一个插入元素之间获得默认构造的元素。
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