1// -*- C++ -*-
2
3// Copyright (C) 2005-2015 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library.  This library is free
6// software; you can redistribute it and/or modify it under the terms
7// of the GNU General Public License as published by the Free Software
8// Foundation; either version 3, or (at your option) any later
9// version.
10
11// This library is distributed in the hope that it will be useful, but
12// WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14// General Public License for more details.
15
16// You should have received a copy of the GNU General Public License
17// along with this library; see the file COPYING3.  If not see
18// <http://www.gnu.org/licenses/>.
19
20
21// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
22
23// Permission to use, copy, modify, sell, and distribute this software
24// is hereby granted without fee, provided that the above copyright
25// notice appears in all copies, and that both that copyright notice
26// and this permission notice appear in supporting documentation. None
27// of the above authors, nor IBM Haifa Research Laboratories, make any
28// representation about the suitability of this software for any
29// purpose. It is provided "as is" without express or implied
30// warranty.
31
32/**
33 * @file hash_initial_size_example.cpp
34 * An example of setting an initial size for a container object.
35 */
36
37/**
38 * This example shows how to set the initial size of a hash-based
39 * container object through its resize-policy object.
40 */
41
42#include <cassert>
43#include <ext/pb_ds/assoc_container.hpp>
44#include <ext/pb_ds/hash_policy.hpp>
45
46using namespace std;
47using namespace __gnu_pbds;
48
49// A simple hash functor.
50// hash could serve instead of this functor, but it is not yet
51// standard everywhere.
52struct int_hash : public unary_function<int, size_t>
53{
54  inline size_t
55  operator()(const int& r_i) const
56  { return r_i; }
57};
58
59int main()
60{
61  // Resize policy type.
62  typedef
63    hash_standard_resize_policy<
64    // Size-policy type.
65    hash_exponential_size_policy<>,
66    // Trigger-policy type.
67    hash_load_check_resize_trigger<>,
68    /* Allow external access to size.
69     *     This is just used in this example for using the
70     *     get_actual_size method (which won't be accessible without
71     *     this flag.
72     */
73    true>
74    resize_policy_t;
75
76  // A collision-probing hash table mapping ints to chars.
77  typedef
78    gp_hash_table<
79    int,
80    char,
81    int_hash,
82    equal_to<
83    int>,
84    // Combining function.
85    direct_mask_range_hashing<>,
86    // Probe function.
87    linear_probe_fn<>,
88    // Resize policy.
89    resize_policy_t>
90    map_t;
91
92  // A resize-policy object with suggested initial size 256.
93  resize_policy_t res(hash_exponential_size_policy<>(256));
94
95  map_t g(int_hash(),
96	  equal_to<int>(),
97	  direct_mask_range_hashing<>(),
98	  linear_probe_fn<>(),
99	  res);
100
101  // Check the actual size of the container object. In this case, this
102  // should be the initial size given by the size policy object.
103  assert(g.get_actual_size() == 256);
104
105  // The logical size of g, though is 0 (it does not contain any elements).
106  assert(g.size() == 0);
107
108  return 0;
109}
110
111