关联容器 — hash_map

template <class Key, class T, class HashFcn = hash<Key>,
          class EqualKey = equal_to<Key>,
          class Alloc = alloc>
class hash_map
{
private:
  typedef hashtable<pair<const Key, T>, Key, HashFcn,
                    select1st<pair<const Key, T> >, EqualKey, Alloc> ht;
  ht rep;     // 底层机制——hash table
  ....
}

template <class Value, class Key, class HashFcn,
          class ExtractKey, class EqualKey,
          class Alloc>
class hashtable {   // hash table数据结构
public:
  typedef Key key_type;
  typedef Value value_type;
 
  ....
  typedef __hashtable_node<Value> node;
  typedef simple_alloc<node, Alloc> node_allocator; // 空间配置器
 
  vector<node*,Alloc> buckets;  // 桶的集合
  ....
}

#include <iostream>
#include <hash_map>
#include <cstring>
 
using namespace std;
using namespace __gnu_cxx;
 
struct eqstr {
    bool operator() (const char *s1, const char *s2) const
    { return strcmp(s1, s2) == 0; }
};
 
int main()
{
    hash_map<const char*, int, hash<const char *>, eqstr> m;
 
    // 两种插入方法
    m["hello"] = 123;
    m["byebye"] = 234;
    m["test"] = 345;
    m.insert(pair<const char *, int>("a", 222));
 
    hash_map<const char*, int, hash<const char *>, eqstr>::iterator iter = m.begin();
 
    for ( ; iter != m.end(); ++iter)
        cout << iter->first << ‘ ‘ << iter->second << endl;
 
    return 0;
}

运行结果：

template <class T>
struct equal_to : public binary_function<T, T, bool> {
    bool operator()(const T& x, const T& y) const { return x == y; }
};