如何使用 std::copy 将一张地图复制到另一张地图?
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代码>?您应该使用成员函数
std::map
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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