nestfriend.cpp

Think in C++ 第二版源码

//: C05:NestFriend.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Nested friends
#include <iostream>
#include <cstring> // memset()
using namespace std;
const int sz = 20;

struct Holder {
private:
  int a[sz];
public:
  void initialize();
  struct Pointer {
  private:
    Holder* h;
    int* p;
  public:
    void initialize(Holder* h);
    // Move around in the array:
    void next();
    void previous();
    void top();
    void end();
    // Access values:
    int read();
    void set(int i);
  };
  friend Holder::Pointer;
};

void Holder::initialize() {
  memset(a, 0, sz * sizeof(int));
}

void Holder::Pointer::initialize(Holder* h) {
  h = h;
  p = h->a;
}

void Holder::Pointer::next() {
  if(p < &(h->a[sz - 1])) p++;
}

void Holder::Pointer::previous() {
  if(p > &(h->a[0])) p--;
}

void Holder::Pointer::top() {
  p = &(h->a[0]);
}

void Holder::Pointer::end() {
  p = &(h->a[sz - 1]);
}

int Holder::Pointer::read() {
  return *p;
}

void Holder::Pointer::set(int i) {
  *p = i;
}

int main() {
  Holder h;
  Holder::Pointer hp, hp2;
  int i;

  h.initialize();
  hp.initialize(&h);
  hp2.initialize(&h);
  for(i = 0; i < sz; i++) {
    hp.set(i);
    hp.next();
  }
  hp.top();
  hp2.end();
  for(i = 0; i < sz; i++) {
    cout << "hp = " << hp.read()
      << ", hp2 = " << hp2.read() << endl;
    hp.next();
    hp2.previous();
  }
} ///:~