Deprecated HP/SGI

Deprecated HP/SGI
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+ The SGI hashing classes hash_set and + hash_set have been deprecated by the + unordered_set, unordered_multiset, unordered_map, + unordered_multimap containers in TR1 and the upcoming C++0x, and + may be removed in future releases. +

The SGI headers

+     <hash_map>
+     <hash_set>
+     <rope>
+     <slist>
+     <rb_tree>
+

are all here; + <hash_map> and <hash_set> + are deprecated but available as backwards-compatible extensions, + as discussed further below. <rope> is the + SGI specialization for large strings ("rope," + "large strings," get it? Love that geeky humor.) + <slist> is a singly-linked list, for when the + doubly-linked list<> is too much space + overhead, and <rb_tree> exposes the red-black + tree classes used in the implementation of the standard maps and + sets. +

Each of the associative containers map, multimap, set, and multiset + have a counterpart which uses a + hashing + function to do the arranging, instead of a strict weak ordering + function. The classes take as one of their template parameters a + function object that will return the hash value; by default, an + instantiation of + hash. + You should specialize this functor for your class, or define your own, + before trying to use one of the hashing classes. +

The hashing classes support all the usual associative container + functions, as well as some extra constructors specifying the number + of buckets, etc. +

Why would you want to use a hashing class instead of the + “normal”implementations? Matt Austern writes: +

+ [W]ith a well chosen hash function, hash tables + generally provide much better average-case performance than + binary search trees, and much worse worst-case performance. So + if your implementation has hash_map, if you don't mind using + nonstandard components, and if you aren't scared about the + possibility of pathological cases, you'll probably get better + performance from hash_map. + +