[英]unordered_map iteration order for the same key
When looping over an std::unordered_map
, STL makes no guarantees on which specific element order is considered. 当循环遍历
std::unordered_map
,STL不保证考虑哪个特定的元素顺序。
My question is about the order of the elements with the same key, I tried it with different compilers and I always receive one after the other if they have same key (example below). 我的问题是关于具有相同密钥的元素的顺序,我尝试使用不同的编译器,并且如果它们具有相同的密钥,我总是一个接一个地接收(例如下面的例子)。 I searched it but I couldn't find.
我搜索了但我找不到。 Is it mentioned somewhere in standards or it is implementation dependent?
它是在标准的某处提到还是依赖于实现?
unordered_multimap<int, int> umap;
umap.insert({30, 9});
umap.insert({10, 1});
umap.insert({20, 5});
umap.insert({30, 8});
umap.insert({20, 4});
umap.insert({10, 2});
for (auto p : umap)
cout << p.first << " " << p.second << endl;
outputs 输出
30 8
30 9
20 4
20 5
10 1
10 2
Yes, it's mentioned in C++11 23.2.5/6: 是的,它在C ++ 11 23.2.5 / 6中提到:
In containers that support equivalent keys, elements with equivalent keys are adjacent to each other in the iteration order of the container.
在支持等效键的容器中,具有等效键的元素在容器的迭代顺序中彼此相邻。
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