libstdc++-v3/testsuite/ext/pb_ds/example/hash_initial_size.cc

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005-2024 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
  46 using namespace std;
  47 using 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.
  52 struct int_hash
  53 {
  54   size_t
  55   operator()(const int& r_i) const
  56   { return r_i; }
  57 };
  58
  59 int 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