Transformの使い方

Transformの機能は、[first 1,first 2]の要素を演算し、結果をresultに格納する
unary operation(1)(一元演算)
  template    OutputIterator transform (InputIterator first1, InputIterator last1,                             OutputIterator  result, UnaryOperation op);
binary operation(2)(二元演算)
template            class OutputIterator, class BinaryOperation>    OutputIterator transform (InputIterator1 first1, InputIterator1 last1,                             InputIterator2  first2, OutputIterator result,                             BinaryOperation binary_op);
 
transformには2つの形式があり、1つは1元オペレータであり、もう1つは2元オペレータである.
一元オペレータの場合は、次のようになります.

template 

 OutputIterator transform (InputIterator first1, InputIterator last1,

                            OutputIteratorresult, UnaryOperator op)

{

  while (first1 != last1) {

   *result = op(*first1);  // or: *result=binary_op(*first1,*first2++);

   ++result; ++first1;

  }

  return result;

}

二元オペレータの場合、各iteratorの意味:
二元オペレータの場合、関数はfirst 1の要素とfirst 2の要素がop演算を行いresultに格納されることを意味する
例:

#include 
#include 
#include 
#include 

// The function object multiplies an element by a Factor
template 
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
      Type operator ( ) ( Type& elem ) const 
      {
         return elem * Factor;
      }
};

int main( )
{	 
   using namespace std;
   vector  v1, v2 ( 7 ), v3 ( 7 );
   vector ::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 ( 2 ) );
   cout << "The elements of the vector v1 multiplied by 2 in place gives:"
        << "
 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 ( 5 ) );
   
   cout << "Multiplying the elements of the vector v1mod
 "
        <<  "by the factor 5 & copying to v2 gives:
 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  ( ) );
   
   cout << "Multiplying elements of the vectors v1mod and v2 pairwise "
        <<  "gives:
 v3 = ( " ;
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )
      cout << *Iter3 << " ";
   cout << ")." << endl;
}