使用std :: map与std :: string keys vs int key的成本？

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我知道单个地图查询最多需要log（N）的时间。但是我想知道，我已经看到了很多使用字符串作为地图键的例子。将std :: string作为键映射到地图而不是int的性能代价是多少？

I know that the individual map queries take a maximum of log(N) time. However I was wondering, I have seen a lot of examples that use strings as map keys. What is the performance cost of associating a std::string as a key to a map instead of an int for example ?

std :: map< ; std :: string，aClass *> someMap; vs std :: map< int，aClass *> someMap;

谢谢！

推荐答案

除了通过比较已经提到的字符串的时间复杂性，每次将项目添加到容器时，字符串键还会导致额外的内存分配。在某些情况下，高度并行系统，全局分配器互斥可能是性能问题的根源。

In addition to the time complexity from comparing strings already mentioned, a string key will also cause an additional memory allocation each time an item is added to the container. In certain cases, e.g. highly parallel systems, a global allocator mutex can be a source of performance problems.

一般来说，你应该选择在你的情况下最有意义的替代品，基于实际性能测试进行优化。很难判断什么是瓶颈。

In general, you should choose the alternative that makes the most sense in your situation, and only optimize based on actual performance testing. It's notoriously hard to judge what will be a bottleneck.