hash_map/unordered_map 中的项目顺序是否稳定?

Is the order of items in a hash_map/unordered_map stable?(hash_map/unordered_map 中的项目顺序是否稳定?)

问题描述

是否保证当一个 hash_map/unordered_map 加载相同的项目时，它们在迭代时将具有相同的顺序?基本上我有一个从文件加载的哈希图，我会定期将有限数量的项目提供给例程，然后释放哈希图.消费完项目后，我将相同的文件重新加载到哈希图中，并希望在我上次停止的点之后获取下一批项目.我停止的点将由钥匙识别.

Is it guaranteed that when a hash_map/unordered_map is loaded with the same items, they will have the same order when iterated? Basically I have a hashmap which I load from a file, and from which I periodically feed a limited number of items to a routine, after which I free the hashmap. After the items are consumed, I re-load the same file to the hashmap and want to get the next batch of items after the point where I stopped the previous time. The point at which I stop would be identified by the key.

推荐答案

从技术上讲，不保证它们按任何特定顺序排列.

Technically no, they are not guaranteed to be in any particular order.

然而，在实践中，鉴于您使用确定性哈希函数，您想要做的应该没问题.

In practice however, given that you use deterministic hash function, what you want to do should be fine.

考虑

std::string name;
std::string value;

std::unordered_map <std::string, std::string> map1;
std::unordered_map <std::string, std::string> map2;

while (read_pair (name, value))
{
    map1[name] = value;
    map2[name] = value;
}

您可以合理地期望 map1 和 map2 中的名称-值对以相同的顺序排列.

you can reasonably expect that name-value pairs in map1 and map2 go in the same order.

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