for_each

应用于每个元素的指定函数对象按范围内的前向序列和函数返回对象。

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

参数

• _First
  解决输入的迭代器第一个元素的位置将对的大小。

• _Last
  解决输入的迭代器通过最终元素的位置一个范围操作。

• _Func
  会应用于该范围内的每个元素的用户定义的函数对象。

返回值

函数对象的副本，从而在应用于所有在范围后的元素。

备注

算法 for_each 非常灵活，允许每个元素的修改一个范围内的不同，用户指定的方式。 Templatized功能可以重用速率已修改的形式传递不同的参数。 用户定义的函数可能累积在算法可以在处理所有后返回该范围内的元素的内部状态中的信息。

该范围引用必须是有效的;所有指针必须dereferenceable，因此，在序列中，最后位置必须是可访问的从开始按增量。

复杂是线性与至多(_Last – _First)进行比较。

示例

// 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;
}

要求

标头: <algorithm>

命名空间: std

请参见

参考

for_each (STL Samples)

标准模板库