| // -*- C++ -*- |
| |
| // Copyright (C) 2005, 2006 Free Software Foundation, Inc. |
| // |
| // This file is part of the GNU ISO C++ Library. This library is free |
| // software; you can redistribute it and/or modify it under the terms |
| // of the GNU General Public License as published by the Free Software |
| // Foundation; either version 2, or (at your option) any later |
| // version. |
| |
| // This library is distributed in the hope that it will be useful, but |
| // WITHOUT ANY WARRANTY; without even the implied warranty of |
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| // General Public License for more details. |
| |
| // You should have received a copy of the GNU General Public License |
| // along with this library; see the file COPYING. If not, write to |
| // the Free Software Foundation, 59 Temple Place - Suite 330, Boston, |
| // MA 02111-1307, USA. |
| |
| // As a special exception, you may use this file as part of a free |
| // software library without restriction. Specifically, if other files |
| // instantiate templates or use macros or inline functions from this |
| // file, or you compile this file and link it with other files to |
| // produce an executable, this file does not by itself cause the |
| // resulting executable to be covered by the GNU General Public |
| // License. This exception does not however invalidate any other |
| // reasons why the executable file might be covered by the GNU General |
| // Public License. |
| |
| // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL. |
| |
| // Permission to use, copy, modify, sell, and distribute this software |
| // is hereby granted without fee, provided that the above copyright |
| // notice appears in all copies, and that both that copyright notice |
| // and this permission notice appear in supporting documentation. None |
| // of the above authors, nor IBM Haifa Research Laboratories, make any |
| // representation about the suitability of this software for any |
| // purpose. It is provided "as is" without express or implied |
| // warranty. |
| |
| /** |
| * @file store_hash_example.cpp |
| * An example showing how to store hash-values with |
| * each entry in a hash-based container. |
| */ |
| |
| /** |
| * This example shows how to configure a hash-based container to store |
| * the hash value of each key along with each entry. This technique |
| * is useful for complex keys (e.g., strings in this example), since |
| * it lowers the cost of collisions. For simpler types (e.g., integers), |
| * where the cost of comparing keys is of the same order as the cost |
| * of comparing hash values, this technique adds unnecessary overhead. |
| */ |
| |
| #include <functional> |
| #include <string> |
| #include <ext/pb_ds/assoc_container.hpp> |
| #include <ext/pb_ds/hash_policy.hpp> |
| |
| using namespace std; |
| using namespace pb_ds; |
| |
| // A string hash functor. |
| struct string_hash : public unary_function<string, size_t> |
| { |
| inline size_t |
| operator()(string str) const |
| { |
| string::const_iterator b = str.begin(); |
| string::const_iterator e = str.end(); |
| |
| size_t hash = 0; |
| while (b != e) |
| { |
| hash *= 5; |
| hash += static_cast<size_t>(*b); |
| ++b; |
| } |
| return hash; |
| } |
| }; |
| |
| int main() |
| { |
| // A collision-chaining hash table mapping strings to ints. |
| typedef |
| cc_hash_table< |
| string, |
| int, |
| string_hash, |
| equal_to<string>, |
| direct_mask_range_hashing<>, |
| hash_standard_resize_policy<>, |
| true> |
| map_t; |
| |
| map_t h; |
| |
| // Use regularly. |
| h["Hello, "] = 0; |
| h["world"] = 1; |
| |
| return 0; |
| } |
| |