statichierarchynavigation.cpp

Thinking in C++, 2nd Edition, Volume 2. 英文doc版 每章源代码

//: C15:StaticHierarchyNavigation.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
// Navigating class hierarchies with static_cast
#include <iostream>
#include <typeinfo>
using namespace std;

class Shape { public: virtual ~Shape() {}; };
class Circle : public Shape {};
class Square : public Shape {};
class Other {};

int main() {
  Circle c;
  Shape* s = &c; // Upcast: normal and OK
  // More explicit but unnecessary:
  s = static_cast<Shape*>(&c);
  // (Since upcasting is such a safe and common
  // operation, the cast becomes cluttering)
  Circle* cp = 0;
  Square* sp = 0;
  // Static Navigation of class hierarchies
  // requires extra type information:
  if(typeid(s) == typeid(cp)) // C++ RTTI
    cp = static_cast<Circle*>(s);
  if(typeid(s) == typeid(sp))
    sp = static_cast<Square*>(s);
  if(cp != 0)
    cout << "It's a circle!" << endl;
  if(sp != 0)
    cout << "It's a square!" << endl;
  // Static navigation is ONLY an efficiency hack;
  // dynamic_cast is always safer. However:
  // Other* op = static_cast<Other*>(s);
  // Conveniently gives an error message, while
  Other* op2 = (Other*)s;
  // does not
} ///:~