在c++中实现LRU缓存-编译错误

我需要在c++中实现LRU缓存。我有这个代码，我有问题，而编译:

#include <iostream>
#include <vector>
#include <hash_map>
using namespace std;
using namespace stdext;
template<class K, class T>
struct LRUCacheEntry
{
    K key;
    T data;
    LRUCacheEntry* prev;
    LRUCacheEntry* next;
};
template<class K, class T>
class LRUCache
{
private:
    hash_map< K, LRUCacheEntry<K,T>* >  _mapping;
    vector< LRUCacheEntry<K,T>* >       _freeEntries;
    LRUCacheEntry<K,T> *            head;
    LRUCacheEntry<K,T> *            tail;
    LRUCacheEntry<K,T> *            entries;
public:
    LRUCache(size_t size){
        entries = new LRUCacheEntry<K,T>[size];
        for (int i=0; i<size; i++)
            _freeEntries.push_back(entries+i);
        head = new LRUCacheEntry<K,T>;
        tail = new LRUCacheEntry<K,T>;
        head->prev = NULL;
        head->next = tail;
        tail->next = NULL;
        tail->prev = head;
    }
    ~LRUCache()
    {
        delete head;
        delete tail;
        delete [] entries;
    }
    void put(K key, T data)
    {
        LRUCacheEntry<K,T>* node = _mapping[key];
        if(node)
        {
            // refresh the link list
            detach(node);
            node->data = data;
            attach(node);
        }
        else{
            if ( _freeEntries.empty() )
            {
                node = tail->prev;
                detach(node);
                _mapping.erase(node->key);
                node->data = data;
                node->key = key;
                attach(node);
            }
            else{
                node = _freeEntries.back();
                _freeEntries.pop_back();
                node->key = key;
                node->data = data;
                _mapping[key] = node;
                attach(node);
            }
        }
    }
    T get(K key)
    {
        LRUCacheEntry<K,T>* node = _mapping[key];
        if(node)
        {
            detach(node);
            attach(node);
            return node->data;
        }
        else return NULL;
    }
private:
    void detach(LRUCacheEntry<K,T>* node)
    {
        node->prev->next = node->next;
        node->next->prev = node->prev;
    }
    void attach(LRUCacheEntry<K,T>* node)
    {
        node->next = head->next;
        node->prev = head;
        head->next = node;
        node->next->prev = node;
    }
};

编译resualt:

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/backward/hash_map:60,
                 from Source.C:3:
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/backward/backward_warning.h:28:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated.
Source.C:6: error: âstdextâ is not a namespace-name
Source.C:6: error: expected namespace-name before â;â token
Source.C:21: error: ISO C++ forbids declaration of âhash_mapâ with no type
Source.C:21: error: expected â;â before â<â token
Source.C: In member function âvoid LRUCache<K, T>::put(K, T)â:
Source.C:46: error: â_mappingâ was not declared in this scope
Source.C: In member function âT LRUCache<K, T>::get(K)â:
Source.C:77: error: â_mappingâ was not declared in this scope

有人能告诉我如何解决"stdext"问题吗?我想它会解决剩下的错误。TNX !