将 std::map 与 std::string 键与 int 键一起使用的成本?-C/C++问题

Cost of using std::map with std::string keys vs int keys?(将 std::map 与 std::string 键与 int 键一起使用的成本?)

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问题描述

我知道单个地图查询最多需要 log(N) 时间.但是我想知道，我已经看到很多使用字符串作为映射键的示例.例如，将 std::string 作为键而不是 int 关联到映射的性能成本是多少?

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::mapsomeMap; vs std::mapsomeMap;

谢谢！

推荐答案

除了已经提到的比较字符串的时间复杂性之外，每次向容器中添加项目时，字符串键还会导致额外的内存分配.在某些情况下，例如高度并行的系统，全局分配器互斥锁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，您应该选择最适合您情况的替代方案，并且仅根据实际性能测试进行优化.众所周知，很难判断什么将成为瓶颈.

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.

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