STL（二）Iterators

• 定义：
  • 是类的对象，用来遍历容器的元素，可被视作指向容器元素的指针。
  • 为获取不同容器元素提供了统一接口（Iterators are central to generic programming because they are an interface between containers and algorithms）
• 类型：
  • container::iterator （read/write iterator）  
  • container::const_iterator （read-only iterator）  
• 操作：（引自：http://www.fredosaurus.com/notes-cpp/stl-iterators/iter-ops.html）
  • Assume C is a container class, containing elements of type T.

  • bool b;
    
    int i;
    
    T value;
    
    C::iterator it, it1, it2;

  • Result	Operator	Description
    Operators for most iterators. Vectors, lists, arrays, ....
    value =	*it;	Use dereference (*) op to get/set value.
    	++it;	Points to next element. Value after update.
    	it++;	Points to next element. Value before update.
    it1 =	it2;	Assignment
    b =	it1 == it2;	Equality comparison.
    b =	it1 != it2;	Inequality.
    Additional operators for bidirectional iterators. Vectors, lists, arrays, ...
    	--it;	Predecrement.
    	it--;	Postdecrement. May be less efficient than predecrement.
    Additional operators for random-access iterators. Vectors and arrays, but not lists.
    it +=	i;	Increments it by i positions.
    it -=	i;	Decrements it by i positions.
    it1 =	it2 + i;	Increments it by i positions.
    it1 =	it2 - i;	Decrements it by i positions.
    value =	it[i];	Returns reference to ith element after it.
    b =	it1 < it2;	Comparison.
    b =	it1 <= it2;	Comparison.
    b =	it1 > it2;	Comparison.
    b =	it1 <= it2;	Comparison.