如何使用 std::copy 将一张地图复制到另一张地图?

2022-01-07 00:00:00 复制 iterator c++ map stl

我想将一个 std::map 的内容复制到另一个.我可以使用 std::copy 吗?显然，以下代码将不起作用:

I would like to copy the content of one std::map into another. Can I use std::copy for that? Obviously, the following code won't work:

int main() {
  typedef std::map<int,double> Map;
  Map m1;
  m1[3] = 0.3;
  m1[5] = 0.5;
  Map m2;
  m2[1] = 0.1;
  std::copy(m1.begin(), m1.end(), m2.begin());
  return 0;
}

这将不起作用，因为 copy 将调用 m2.begin() 上的 operator* 来取消引用"它并分配一个值(所有值的类型都是 std::pair).然后调用operator++移动到m2中的下一个空格.由于 const int 中的 const 并且没有为任何新元素保留空间，因此这两个操作都不起作用.

This won't work because copy will call operator* on m2.begin() to "dereference" it and assign a value (all values are of type std::pair<const int, double>). Then it will call operator++ to move to the next space in m2. Both of these operations don't work because of the const in const int and there is no space reserved for any new elements.

有什么方法可以让它与 std::copy 一起工作?

Is there any way to make it work with std::copy?

谢谢！

推荐答案

您可以使用 GMan 的回答 --- 但问题是，为什么您要使用 std::copy?您应该使用成员函数 std::map::insert 代替.

You can use GMan's answer --- but the question is, why do you want to use std::copy? You should use the member function std::map<k, v>::insert instead.

m2.insert(m1.begin(), m1.end());

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