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21 void assignin first in last firstlast void

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Unformatted text preview: cn 专门化的容器和迭代器 写容器上迭代的代码 int count(Itor<char>& ii, char term) { int c = 0; for(char* p = ii.first(); p; p=ii.next()) if(*p==term) c++; return c; } 注意,这种方式引起了一次虚函数的调用,很多情 况下,这种额外开销是无关大局的,但是,这种方 式对于标准库不合适 本例中:Itor甚至可以在Vector和List设计和实现 很久以后才提供 Beijing University of Posts & Telecommunications Beijing [email protected] 16.2.2 有基类的容器 Simula采用如下风格定义了它的标准容器 struct Link{ Link* pre; Link* suc; }; class List{ Link* head; Link* curr; public: Link* get(); void put(Link*); }; // 一个List就是一个Link的 表,可以保存由Link派生的任 何类型的对象 class Ship:public Link{/*...*/}; void f(List* lst){ while(Link* po=lst->get()){ if(Ship* ps = dynamic_cast<Ship*>(po)){ //... } else { //... } } } Beijing University of Posts & Telecommunications Beijing [email protected] 有基类的容器 常见情况是定义一个公共容器类型 class Container:public Object{ // 公共容器类型 public: virtual Object* get(); virtual void put(Object*); virtual Object*& operator(size_t); }; // 操作全部是虚的 class List:public Container{ public: Object* get(); void put(Object*); }; class Vector:public...
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