multiset1.cpp

Think in C++ 第二版源码

//: C20:MultiSet1.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Demonstration of multiset behavior
#include <iostream>
#include <set>
#include <algorithm>
#include <ctime>
using namespace std;

class X {
  char c; // Used in comparison
  int i; // Not used in comparison
  // Don't need default constructor and operator=
  X();
  X& operator=(const X&);
  // Usually need a copy-constructor (but the
  // synthesized version works here)
public:
  X(char cc, int ii) : c(cc), i(ii) {}
  // Notice no operator== is required
  friend bool operator<(const X& x, const X& y) {
    return x.c < y.c;
  }
  friend ostream& operator<<(ostream& os, X x) {
    return os << x.c << ":" << x.i;
  }
};

class Xgen {
  static int i;
  // Number of characters to select from:
  static const int span = 6;
public:
  Xgen() { srand(time(0)); }
  X operator()() {
    char c = 'A' + rand() % span;    
    return X(c, i++);
  }
};

int Xgen::i = 0;

typedef multiset<X> Xmset;
typedef Xmset::const_iterator Xmit;

int main() {
  Xmset mset;
  // Fill it with X's:
  generate_n(inserter(mset, mset.begin()), 
    25, Xgen());
  // Initialize a regular set from mset:
  set<X> unique(mset.begin(), mset.end());
  copy(unique.begin(), unique.end(), 
    ostream_iterator<X>(cout, " "));
  cout << "\n----\n";
  // Iterate over the unique values:
  for(set<X>::iterator i = unique.begin();
      i != unique.end(); i++) {
    pair<Xmit, Xmit> p = mset.equal_range(*i);
    copy(p.first, p.second, 
      ostream_iterator<X>(cout, " "));
    cout << endl;
  }
} ///:~