for_each

套用至每個項目的指定函式物件超出範圍內的向前順序並傳回函式物件。

template<class InputIterator, class Function> 
   Function for_each( 
      InputIterator _First,  
      InputIterator _Last,  
      Function _Func 
   );

參數

• _First
  輸入定址的 Iterator 第一個項目位置範圍起作用。

• _Last
  輸入定址的 Iterator 將最後一個項目的位置會介於起作用。

• _Func
  套用至這個範圍內的每個項目的使用者定義的函式物件。

傳回值

函式物件的複本，然後再套用至所有在這個範圍後的項目。

備註

for_each 演算法非常有彈性，讓每個項目的修改在某個範圍內的不同，使用者指定的模式。 Templatized 函式可能會重複使用以修改過的形式傳遞不同的參數。 使用者定義的函式可能會累積在演算法可能會在處理所有後傳回在這個範圍的元素內的狀態中的資訊。

參考的範圍必須是有效的;所有指標必須 dereferenceable，必要時，在序列中，最後一個位置必須取用開頭 (由增量。

複雜是線性與至多 (_Last – _First) 比較。

範例

// alg_for_each.cpp
// compile with: /EHsc
#include <vector>
#include <algorithm>
#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
   void operator ( ) ( Type& elem ) const
   {
      elem *= Factor;
   }
};

// The function object to determine the average
class Average
{
private:
   long num;      // The number of elements
   long sum;      // The sum of the elements
public:
   // Constructor initializes the value to multiply by
   Average ( ) : num ( 0 ) , sum ( 0 )
   {
   }

   // The function call to process the next elment
   void operator ( ) ( int elem ) \
   {
      num++;      // Increment the element count
      sum += elem;   // Add the value to the partial sum
   }

   // return Average
   operator double ( )
   {
      return  static_cast <double> (sum) /
      static_cast <double> (num);
   }
};

int main( )
{
   using namespace std;
   vector <int> v1;
   vector <int>::iterator Iter1;

   // 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;

   // Using for_each to multiply each element by a Factor
   for_each ( v1.begin ( ) , v1.end ( ) , MultValue<int> ( -2 ) );

   cout << "Multiplying the elements of the vector v1\n "
        <<  "by the factor -2 gives:\n v1mod1 = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // The function object is templatized and so can be
   // used again on the elements with a different Factor
   for_each (v1.begin ( ) , v1.end ( ) , MultValue<int> (5 ) );

   cout << "Multiplying the elements of the vector v1mod\n "
        <<  "by the factor 5 gives:\n v1mod2 = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // The local state of a function object can accumulate
   // information about a sequence of actions that the
   // return value can make available, here the Average
   double avemod2 = for_each ( v1.begin ( ) , v1.end ( ) ,
      Average ( ) );
   cout << "The average of the elements of v1 is:\n Average ( v1mod2 ) = "
        << avemod2 << "." << endl;
}

需求

標頭：<algorithm>

命名空間: std

請參閱

參考

for_each (STL 範例)

標準樣板程式庫