recycle2.cpp

C语言数值算法程序大全（第二版）,课本文件

//: C08:Recycle2.cpp
// From "Thinking in C++, 2nd Edition, Volume 2"
// by Bruce Eckel & Chuck Allison, (c) 2003 MindView, Inc.
// Available at www.BruceEckel.com.
// A Trash Recycler
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <map>
#include <typeinfo>
#include <utility>
#include <vector>
#include "../purge.h"
using namespace std;

class Trash {
  float _weight;
public:
  Trash(float wt) : _weight(wt) {}
  virtual float value() const = 0;
  float weight() const { return _weight; }
  virtual ~Trash() { cout << "~Trash()\n"; }
};

class Aluminum : public Trash {
  static float val;
public:
  Aluminum(float wt) : Trash(wt) {}
  float value() const { return val; }
  static void value(float newval) {
    val = newval;
  }
};
float Aluminum::val = 1.67;

class Paper : public Trash {
  static float val;
public:
  Paper(float wt) : Trash(wt) {}
  float value() const { return val; }
  static void value(float newval) {
    val = newval;
  }
};
float Paper::val = 0.10;

class Glass : public Trash {
  static float val;
public:
  Glass(float wt) : Trash(wt) {}
  float value() const { return val; }
  static void value(float newval) {
    val = newval;
  }
};
float Glass::val = 0.23;

// Comparator for type_info pointers
struct TInfoLess {
  bool operator()(const type_info* t1, const type_info* t2) 
  const {
    return t1->before(*t2);
  }
};
typedef map<const type_info*, vector<Trash*>, TInfoLess> 
  TrashMap;

// Sums up the value of the Trash in a bin:
void sumValue(const TrashMap::value_type& p, ostream& os) {
  vector<Trash*>::const_iterator tally = p.second.begin();
  float val = 0;
  while(tally != p.second.end()) {
    val += (*tally)->weight() * (*tally)->value();
    os << "weight of "
        << p.first->name()  // type_info::name()
        << " = " << (*tally)->weight() << endl;
    tally++;
  }
  os << "Total value = " << val << endl;
}

int main() {
  srand(time(0)); // Seed random number generator
  TrashMap bin;
  // Fill up the Trash bin:
  for(int i = 0; i < 30; i++) {
    Trash* tp;
    switch(rand() % 3) {
      case 0 :
        tp = new Aluminum((rand() % 1000)/10.0);
        break;
      case 1 :
        tp = new Paper((rand() % 1000)/10.0);
        break;
      case 2 :
        tp = new Glass((rand() % 1000)/10.0);
        break;
    }
    bin[&typeid(*tp)].push_back(tp);
  }
  // Print sorted results
  for (TrashMap::iterator p = bin.begin();
       p != bin.end(); ++p) {
    sumValue(*p, cout);
    purge(p->second);
  }
} ///:~