调整外部向量大小是否会复制内部向量？ [英] Does resizing an outer vector copies the inner vector?

问题描述

假设您有向量向量：

vector<vector<string> > v;

到不同的地址），例如通过做很多 v.push_back（），内部向量的内部数组也被复制（因为向量的拷贝构造器通常拷贝内部数组），或者C ++有一个方法来调整外部向量而不复制一切递归？

when the internal array of the outer vector is resized (and suppose the internal array also have to be reallocated to a different address), for example by doing lots of v.push_back(), does the internal array of the inner vectors get copied as well (because vector's copy constructor usually copies the internal array), or does C++ have a way to resize the outer vector without copying everything recursively?

C ++ 11移动构造函数是否会影响这？这是否取决于STL实现？

Does C++11 move constructor affect this? Does this depend on the STL implementation?

推荐答案

是的，在C ++ 03中，需要外部向量。在C ++ 11中，它们被移动。这取决于实现，只要实现是正确的。如果实现正确，这是行为。

Yes, in C++03, the inner vectors are copied when a reallocation is needed for the outer vector. In C++11, they are moved. It depends on the implementation only so far as the implementation being correct. If the implementation is correct, this is the behavior.

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