矢量C ++地图

Question

嗨，如果我用C ++创建了类型为map<int, vec<double>>的STL映射，向量是否存储在连续放置在内存中的不同键下？

Answer 1

从技术上讲，这将取决于map的实现，但是通常，map被实现为Tree，因此由于tree数据结构的性质，存储在内存中不是连续的。

Answer 2

No. ^*

A map dynamically allocates elements as required. So each vector could be placed anywhere in memory (and may move over time).

Remember also that the element storage within the vector itself is also dynamically allocated. So even if you just created a straightfoward std::vector<double> my_vectors[10] , the elements themsleves would not be contiguous between the individual vectors.

_{* An implementation could conceivably allocate from an array-backed store, but you wouldn't be able to rely on this behaviour. So it's best to assume "no".}