iterator adapter inserter

1.insert_iterator

这个adapter将iterator的赋值（assign）操作变为安插（insert操作），并将iterator右移一个位置。如此便可让user连续执行[表面上assign而实际上insert]的行为。

template <class _Container>
class insert_iterator {
protected:
  _Container* container; //底层容器
  typename _Container::iterator iter;
public:
  typedef _Container          container_type;
  typedef output_iterator_tag iterator_category;//注意类型
  typedef void                value_type;
  typedef void                difference_type;
  typedef void                pointer;
  typedef void                reference;

  insert_iterator(_Container& __x, typename _Container::iterator__i)
    : container(&__x),iter(__i) {}
  insert_iterator<_Container>&
  operator=(const typename _Container::value_type& __value) {
    iter = container->insert(iter, __value); //关键：转调用insert()
    ++iter; //令insert_iterator永远跟随其target贴身移动
    return *this;
  }
  insert_iterator<_Container>& operator*() { return *this; }
  insert_iterator<_Container>& operator++() { return *this; }
  insert_iterator<_Container>& operator++(int) { return *this; }

};

2.inserter

辅助函式，帮助user使用inserter_iterator

template <class _Container, class _Iterator>
inline
insert_iterator<_Container> inserter(_Container&__x, _Iterator__i)
{
  typedef typename _Container::iterator __iter;
  return insert_iterator<_Container>(__x, __iter(__i));
}

3.copy

template<class InputIterator,

             class OutputIterator>

OutputIterator

          copy(InputIterator first,InputIterator last,OutputIterator result)

{

              while(first != last) {

                      *result = *first;

                      ++result ; ++first;

               }

               return result;

}

4.示例

http://www.cplusplus.com/reference/iterator/inserter/

// inserter example#include <iostream>     // std::cout#include <iterator>     // std::front_inserter#include <list>         // std::list#include <algorithm>    // std::copyint main () {  std::list<int> foo,bar;  for (int i=1; i<=5; i++)  { foo.push_back(i); bar.push_back(i*10); }  std::list<int>::iterator it = foo.begin();  advance (it,3);  std::cout << "foo contains:";  for ( std::list<int>::iterator it = foo.begin(); it!= foo.end(); ++it )  std::cout << ' ' << *it;  std::cout << '\n';    std::cout << "bar contains:";  for ( std::list<int>::iterator it = bar.begin(); it!= bar.end(); ++it )  std::cout << ' ' << *it;  std::cout << '\n';  std::copy (bar.begin(),bar.end(),std::inserter(foo,it));  std::cout << "foo contains:";  for ( std::list<int>::iterator it = foo.begin(); it!= foo.end(); ++it )  std::cout << ' ' << *it;  std::cout << '\n';  return 0;}

执行结果：