chapter11-19.cpp

C++STL程序员开发指南

//文件名:CHAPTER11-19.cpp
#include <vector>
#include <algorithm>
#include <functional>
#include <iostream>
// The function object multiplies an element by a Factor
template <class Type>
class MultValue
{
   private:
      Type Factor;   // The value to multiply by
   public:
      // Constructor initializes the value to multiply by
      MultValue ( const Type& _Val ) : Factor ( _Val ) {      }
      // The function call for the element to be multiplied
      int operator ( ) ( Type& elem ) const {         return elem * Factor;      }
};
int main( )
{
   using namespace std;
   vector <int> v1, v2 ( 7 ), v3 ( 7 );
   vector <int>::iterator Iter1, Iter2 , Iter3;
   // Constructing vector v1
   int i;
   for ( i = -4 ; i <= 2 ; i++ ) {v1.push_back(  i ); }
   cout << "Original vector  v1 = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ ) cout << *Iter1 << " ";
   cout << ")." << endl;
   // Modifying the vector v1 in place
   transform (v1.begin ( ) , v1.end ( ) , v1.begin ( ) , MultValue<int> ( 2 ) );
   cout << "The elements of the vector v1 multiplied by 2 in place gives:"<< "\n v1mod = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ ) cout << *Iter1 << " ";
   cout << ")." << endl;
   // Using transform to multiply each element by a factor of 5
   transform ( v1.begin ( ) , v1.end ( ) , v2.begin ( ) , MultValue<int> ( 5 ) );
   cout << "Multiplying the elements of the vector v1mod\n "
        <<  "by the factor 5 & copying to v2 gives:\n v2 = ( " ;
   for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ )cout << *Iter2 << " ";
   cout << ")." << endl;
   // The second version of transform used to multiply the 
   // elements of the vectors v1mod & v2 pairwise
   transform ( v1.begin ( ) , v1.end ( ) ,  v2.begin ( ) , v3.begin ( ) , multiplies <int> ( ) );
   cout << "Multiplying elements of the vectors v1mod and v2 pairwise "<<  "gives:\n v3 = ( " ;
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )
      cout << *Iter3 << " ";
   cout << ")." << endl;
}