ceph/src/boost/libs/container_hash/examples/point.cpp

   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:
  23     point() : x(0), y(0) {}
  24     point(int x, int y) : x(x), y(y) {}
  25
  26     bool operator==(point const& other) const
  27     {
  28         return x == other.x && y == other.y;
  29     }
  30
  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
  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