A recent talk about unordered_map in C++ made me realize that I should use unordered_map for most cases where I used map before, because of the efficiency of lookup ( amortized O(1) vs. O(log n) ). Most times I use a map, I use either int or std::string as the key type; hence, I've got no problems with the definition of the hash function. The more I thought about it, the more I came to realize that I can't find any reason of using a std::map over a std::unordered_map in the case of keys with simple types -- I took a look at the interfaces, and didn't find any significant differences that would impact my code.
因此，问题是:是否有任何真正的理由使用std::map而不是std::unordered_map在简单类型的情况下，如int和std::string?
我是从严格的编程角度提出这个问题的——我知道它并不是完全标准的，而且它可能会给移植带来问题。
另外，我认为正确答案之一可能是“对于较小的数据集更有效”，因为开销更小(是真的吗?)——因此，我希望将这个问题限制在键数量非普通的情况下(>1 024)。
编辑:哦，我忘记了显而易见的(感谢GMan!)——是的，地图当然是有序的——我知道，我正在寻找其他原因。
