smartpointer.cpp

来自「thingking in c++（C++编程思想） 各章节课后练习的答案」· C++ 代码 · 共 65 行

//: C12:SmartPointer.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
#include <iostream>
#include <vector>
#include "../require.h"
using namespace std;

class Obj {
  static int i, j;
public:
  void f() const { cout << i++ << endl; }
  void g() const { cout << j++ << endl; }
};

// Static member definitions:
int Obj::i = 47;
int Obj::j = 11;

// Container:
class ObjContainer {
  vector<Obj*> a;
public:
  void add(Obj* obj) { a.push_back(obj); }
  friend class SmartPointer;
};

class SmartPointer {
  ObjContainer& oc;
  int index;
public:
  SmartPointer(ObjContainer& objc) : oc(objc) {
    index = 0;
  }
  // Return value indicates end of list:
  bool operator++() { // Prefix
    if(index >= oc.a.size()) return false;
    if(oc.a[++index] == 0) return false;
    return true;
  }
  bool operator++(int) { // Postfix
    return operator++(); // Use prefix version
  }
  Obj* operator->() const {
    require(oc.a[index] != 0, "Zero value "
      "returned by SmartPointer::operator->()");
    return oc.a[index];
  }
};

int main() {
  const int sz = 10;
  Obj o[sz];
  ObjContainer oc;
  for(int i = 0; i < sz; i++)
    oc.add(&o[i]); // Fill it up
  SmartPointer sp(oc); // Create an iterator
  do {
    sp->f(); // Pointer dereference operator call
    sp->g();
  } while(sp++);
} ///:~