example227.cpp

Data Abstraction & Problem Solving with C++源码

#include <list>
#include <iostream>
#include <string>
using namespace std;

// define a list of pointer strings
typedef list<string*, allocator<string*> > STRING_PTR;

// override the default behavior of sort
template<> struct std::greater<string*>
{ 
      // override operator() to create a function object  
      bool operator() (string* s1, string *s2)
      {
         return (*s1) > (*s2);
      }
};

int main()
{     
      // create a list of pointer strings and a list iterator
      STRING_PTR groceryList;
      STRING_PTR::iterator i;

      // create pointers to strings in a random order
      // insert the string pointers to the end of the list 
      string* str = new string ("apples");
      groceryList.insert(groceryList.end(), str);
      str = new string ("bread");
      groceryList.insert(groceryList.end(), str);
      str = new string ("juice");
      groceryList.insert(groceryList.end(), str);
      str = new string ("carrots");
      groceryList.insert(groceryList.end(), str);

      cout << "Number of items on my grocery list: " 
           << groceryList.size() << endl;

      // sort with the overridden function object
      groceryList.sort(greater<string*>());

      // print out the list of strings
      cout << "Items after the predicate sort are:" << endl;
      i = groceryList.begin();
      while (i != groceryList.end())
      (   cout << (*(*i)).c_str() << endl;
          i++;
      }
}