examples/containers/unordered_map1.cpp

This example code is explained in the STXXL Unordered Map (Hash Map) section

/***************************************************************************
 * examples/containers/unordered_map1.cpp
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2013 Daniel Feist <[email protected]>
 * Copyright (C) 2014 Timo Bingmann <[email protected]>
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

//! [example]
#include <stxxl/unordered_map>
#include <iostream>

//! [hash]
struct HashFunctor
{
 size_t operator () (int key) const
 {
 // a simple integer hash function
 return (size_t)(key * 2654435761u);
 }
};
//! [hash]

//! [comparator]
struct CompareLess
{
 bool operator () (const int& a, const int& b) const
 { return a < b; }

 static int min_value() { return std::numeric_limits<int>::min(); }
 static int max_value() { return std::numeric_limits<int>::max(); }
};
//! [comparator]

int main()
{
//! [construction]
#define SUB_BLOCK_SIZE 8192
#define SUB_BLOCKS_PER_BLOCK 256

 // template parameter <KeyType, MappedType, HashType, CompareType, SubBlockSize, SubBlocksPerBlock>
 typedef stxxl::unordered_map<
 int, char, HashFunctor, CompareLess, SUB_BLOCK_SIZE, SUB_BLOCKS_PER_BLOCK
 > unordered_map_type;

 // constructor: use defaults for all parameters
 unordered_map_type my_map;
//! [construction]

 // insert some items and delete one
 my_map.insert(std::make_pair(1, 'a'));
 my_map.insert(std::make_pair(2, 'b'));
 my_map.insert(std::make_pair(3, 'c'));
 my_map.insert(std::make_pair(4, 'd'));

 my_map.erase(3);

 // iterate over all items in the unordered_map
 unordered_map_type::iterator iter;

 std::cout << "my_map contains:\n";
 for (iter = my_map.begin(); iter != my_map.end(); ++iter)
 {
 std::cout << iter->first << " => " << iter->second << std::endl;
 }

 // direct operator[] access to items
 std::cout << "my_map[2] = " << my_map[2] << std::endl;

 // efficient bulk-insert into hash map by sorting by hash keys
 std::vector<unordered_map_type::value_type> value_array;

 for (int i = 0; i < 128; ++i)
 value_array.push_back(std::make_pair(i, (char)i));

 my_map.insert(value_array.begin(), value_array.end(), 8 * 1024 * 1024);

 // check results of insertion
 std::cout << "my_map[42] = " << my_map[42] << std::endl;
 std::cout << "my_map.size() = " << my_map.size() << std::endl;

 return 0;
}
//! [example]