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// -*- C++ -*-
// Copyright (C) 2005-2018 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;
}
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