C++，复制集到向量

C++, copy set to vector(C++，复制集到向量)

问题描述

我需要将 std::set 复制到 std::vector:

I need to copy std::set to std::vector:

std::set <double> input;
input.insert(5);
input.insert(6);

std::vector <double> output;
std::copy(input.begin(), input.end(), output.begin()); //Error: Vector iterator not dereferencable

问题出在哪里?

推荐答案

你需要使用一个back_inserter:

std::copy(input.begin(), input.end(), std::back_inserter(output));

std::copy 不会将元素添加到您要插入的容器中:它不能；它只有一个进入容器的迭代器.因此，如果将输出迭代器直接传递给 std::copy，则必须确保它指向的范围至少足以容纳输入范围.

std::copy doesn't add elements to the container into which you are inserting: it can't; it only has an iterator into the container. Because of this, if you pass an output iterator directly to std::copy, you must make sure it points to a range that is at least large enough to hold the input range.

std::back_inserter 创建一个输出迭代器，该迭代器在容器上为每个元素调用 push_back，因此每个元素都插入到容器中.或者，您可以在 std::vector 中创建足够数量的元素来保存被复制的范围:

std::back_inserter creates an output iterator that calls push_back on a container for each element, so each element is inserted into the container. Alternatively, you could have created a sufficient number of elements in the std::vector to hold the range being copied:

std::vector<double> output(input.size());
std::copy(input.begin(), input.end(), output.begin());

或者，您可以使用 std::vector 范围构造函数:

Or, you could use the std::vector range constructor:

std::vector<double> output(input.begin(), input.end()); 

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