nestfrnd.cpp

来自「Thinking in C++ 2nd edition source code 」· C++ 代码 · 共 89 行

//: C05:Nestfrnd.cpp
// From Thinking in C++, 2nd Edition
// at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Nested friends
#include <cstdio>
#include <cstring> // memset()
using namespace std;
#define 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++) {
    printf("hp = %d, hp2 = %d\n",
           hp.read(), hp2.read());
    hp.next();
    hp2.previous();
  }
} ///:~