C++ 中的字典/哈希表对象？
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Dictionary/HashTable Object in C++?
提问by cam
I'm looking for a HashTable or Dictionary implementation in C++ that has similar functionality to the one in C#? Does the STL contain an object like this and how would I use it?
我正在寻找 C++ 中的 HashTable 或 Dictionary 实现，其功能与 C# 中的功能相似？STL 是否包含这样的对象，我将如何使用它？
采纳答案by Dean Harding
Actually, to be exactly the same as .NET's Dictionary/Hashtable, what you want is hash_mapor unordered_map(std::mapis implemented as a binary tree), hash_mapis an extension to the SC++L. Most compilers that I know of come with hash_map, though, and boost obviously has unordered_mapuntil C++0x is available in all compilers, so you should just be able to use it without trouble.
实际上，与.NET 的Dictionary/Hashtable 完全相同，您想要的是hash_map或unordered_map（std::map实现为二叉树）， hash_map是SC++L 的扩展。hash_map不过，我所知道的大多数编译器都带有，而 boost 显然unordered_map在所有编译器中都可以使用 C++0x 之前，所以您应该能够毫无困难地使用它。
回答by gnud
The STL std::mapcan be used to build a dictionary. std::mapis usually implemented as a search tree, not a hash table. That means both lookup and insertion has different perfomance characteristics than C#'s HashMap- for very large maps, average lookup will be slower, especially if the objects in the map are fragmented in memory.
STLstd::map可用于构建字典。std::map通常实现为搜索树，而不是哈希表。这意味着查找和插入都具有与 C# 不同的性能特征HashMap- 对于非常大的映射，平均查找会更慢，特别是如果映射中的对象在内存中碎片化。
In the TR1 of the new c++ standard, you have std::tr1::unordered_mapand std::tr1::unordered_multimap, which will usually be implemented using a hash table. If your compiler does not provide those libraries, you can use the implementation from http://www.boost.org/.
在新的 c++ 标准的 TR1 中，您有std::tr1::unordered_map和std::tr1::unordered_multimap，通常使用哈希表来实现。如果您的编译器不提供这些库，您可以使用http://www.boost.org/ 中的实现。
Yet another alternative is Google's sparse_hash.
另一种选择是谷歌的sparse_hash.
