| // -*- C++ -*- |
| |
| // Copyright (C) 2005-2021 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 3, 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 COPYING3. If not see |
| // <http://www.gnu.org/licenses/>. |
| |
| |
| // 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 hash_initial_size_example.cpp |
| * An example of setting an initial size for a container object. |
| */ |
| |
| /** |
| * This example shows how to set the initial size of a hash-based |
| * container object through its resize-policy object. |
| */ |
| |
| #include <cassert> |
| #include <ext/pb_ds/assoc_container.hpp> |
| #include <ext/pb_ds/hash_policy.hpp> |
| |
| using namespace std; |
| using namespace __gnu_pbds; |
| |
| // A simple hash functor. |
| // hash could serve instead of this functor, but it is not yet |
| // standard everywhere. |
| struct int_hash : public unary_function<int, size_t> |
| { |
| inline size_t |
| operator()(const int& r_i) const |
| { return r_i; } |
| }; |
| |
| int main() |
| { |
| // Resize policy type. |
| typedef |
| hash_standard_resize_policy< |
| // Size-policy type. |
| hash_exponential_size_policy<>, |
| // Trigger-policy type. |
| hash_load_check_resize_trigger<>, |
| /* Allow external access to size. |
| * This is just used in this example for using the |
| * get_actual_size method (which won't be accessible without |
| * this flag. |
| */ |
| true> |
| resize_policy_t; |
| |
| // A collision-probing hash table mapping ints to chars. |
| typedef |
| gp_hash_table< |
| int, |
| char, |
| int_hash, |
| equal_to< |
| int>, |
| // Combining function. |
| direct_mask_range_hashing<>, |
| // Probe function. |
| linear_probe_fn<>, |
| // Resize policy. |
| resize_policy_t> |
| map_t; |
| |
| // A resize-policy object with suggested initial size 256. |
| resize_policy_t res(hash_exponential_size_policy<>(256)); |
| |
| map_t g(int_hash(), |
| equal_to<int>(), |
| direct_mask_range_hashing<>(), |
| linear_probe_fn<>(), |
| res); |
| |
| // Check the actual size of the container object. In this case, this |
| // should be the initial size given by the size policy object. |
| assert(g.get_actual_size() == 256); |
| |
| // The logical size of g, though is 0 (it does not contain any elements). |
| assert(g.size() == 0); |
| |
| return 0; |
| } |
| |