std :: multimap< key，value>之间有什么区别？和std :: map< key，std :: set< value> > [英] What's the difference between std::multimap<key, value> and std::map<key, std::set<value> >

问题描述

我发现他们有一个键和多个值是唯一的。

I found that they have one key and multiple values which is unique.

推荐答案

值），其中key和value都可以出现多次。

The multimap stores pairs of (key, value) where both key and value can appear several times.

map< key，set< value>> 只会为特定键存储每个值一次。为了做到这一点，它必须能够比较值，而不仅仅是键。

The map<key, set<value>> will only store each value once for a specific key. To do that, it will have to be able to compare the values, not just the keys.

根据您的应用程序，如果相等的值相等，或者如果您希望单独存储它们。也许它们包含不同的字段，但不参与该集合的比较。

It depends on your application if the values that compare equal are equivalent, or if you wish to store them separately anyway. Perhaps they contain fields that are different but do not take part in the comparison for the set.

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