map和hash_map在C ++ [英] map vs. hash_map in C++

问题描述

我在C ++中有一个问题， hash_map 和 map 我理解 map 是在STL，但 hash_map 不是一个标准。

I have a question with hash_map and map in C++. I understand that map is in STL, but hash_map is not a standard. What's the difference between the two?

推荐答案

它们是以非常不同的方式实现的。

They are implemented in very different ways.

hash_map （在TR1和Boost中使用 unordered_map ;使用那些）

hash_map (unordered_map in TR1 and Boost; use those instead) use a hash table where the key is hashed to a slot in the table and the value is stored in a list tied to that key.

map 实现为平衡的二叉搜索树（通常是红/黑树）。

map is implemented as a balanced binary search tree (usually a red/black tree).

unordered_map 用于访问集合的已知元素的更好的性能，但是 map 将具有另外有用的特征（例如，以排序顺序存储，这允许从开始到完成的遍历）。 unordered_map 在插入和删除时比映射更快。

An unordered_map should give slightly better performance for accessing known elements of the collection, but a map will have additional useful characteristics (e.g. it is stored in sorted order, which allows traversal from start to finish). unordered_map will be faster on insert and delete than a map.

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