1
2 // Copyright 2005 Daniel James.
3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
5
6 // Force use of assert.
7 #if defined(NDEBUG)
8 #undef NDEBUG
9 #endif
10
11 #include <boost/container_hash/hash.hpp>
12 #include <cassert>
13
14 // This example illustrates how to use boost::hash_combine to generate a hash
15 // value from the different members of a class. For full details see the hash
16 // tutorial.
17
18 class point
19 {
20 int x;
21 int y;
22 public:
point()23 point() : x(0), y(0) {}
point(int x,int y)24 point(int x, int y) : x(x), y(y) {}
25
operator ==(point const & other) const26 bool operator==(point const& other) const
27 {
28 return x == other.x && y == other.y;
29 }
30
hash_value(point const & p)31 friend std::size_t hash_value(point const& p)
32 {
33 std::size_t seed = 0;
34 boost::hash_combine(seed, p.x);
35 boost::hash_combine(seed, p.y);
36
37 return seed;
38 }
39 };
40
main()41 int main()
42 {
43 boost::hash<point> point_hasher;
44
45 point p1(0, 0);
46 point p2(1, 2);
47 point p3(4, 1);
48 point p4 = p1;
49
50 assert(point_hasher(p1) == point_hasher(p4));
51
52 // These tests could legally fail, but if they did it'd be a pretty bad
53 // hash function.
54 assert(point_hasher(p1) != point_hasher(p2));
55 assert(point_hasher(p1) != point_hasher(p3));
56
57 return 0;
58 }
59
60