How to define your own container and iterator

I want to define a simple wrapper class of “std” container. The meaning of the following code is to provide a Qt style container interface for some legacy C++ code segments with Qt. The key point below is

typedef typename map<KEY,VALUE>::iterator iterator;

Because the compiler does not know the following token, so we need explicitly declare “typename” to tell the compiler that the coming token is the name of a type.

The following is the whole declaration and implementation. 

   1:  #ifndef MYMAP_H

   2:  #define MYMAP_H

   3:   

   4:  #include <map>

   5:  using namespace std;

   6:   

   7:  template <class KEY, class VALUE>

   8:  class MyMap

   9:  {

  10:  public:

  11:      MyMap();

  12:      bool contains( KEY data );

  13:      VALUE value( KEY data );

  14:      void insert( KEY key, VALUE value );

  15:      typedef typename map<KEY,VALUE>::iterator iterator;

  16:  private:

  17:      map<KEY,VALUE> _data;

  18:  };

  19:   

  20:  template<class KEY, class VALUE>

  21:  MyMap<KEY, VALUE>::MyMap()

  22:  {

  23:      return;

  24:  }

  25:   

  26:  template<class KEY, class VALUE>

  27:  bool MyMap<KEY, VALUE>::contains( KEY data )

  28:  {

  29:      MyMap<KEY, VALUE>::iterator iter = this->_data.find( data );

  30:      if( iter != this->_data.end() )

  31:      {

  32:          return true;

  33:      }

  34:      else

  35:      {

  36:          return false;

  37:      }

  38:  }

  39:  //

  40:  template<class KEY, class VALUE>

  41:  VALUE MyMap<KEY, VALUE>::value( KEY data )

  42:  {

  43:      MyMap<KEY, VALUE>::iterator iter = this->_data.find( data );

  44:      if( iter != this->_data.end() )

  45:      {

  46:          return iter->second;

  47:      }

  48:      else

  49:      {

  50:          return 0;

  51:      }

  52:  }

  53:  //

  54:  template<class KEY, class VALUE>

  55:  void MyMap<KEY, VALUE>::insert( KEY key, VALUE value )

  56:  {

  57:      this->_data.insert( make_pair( key, value ) );

  58:      return;

  59:  }

  60:   

  61:  #endif