for_each
套用至每個項目上執行指定的函式物件中某個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
處理輸入的 Iterator 第一個項目的位置會在的範圍。_Last
處理輸入的 Iterator 超過最後一個項目的位置是在這個範圍可供操作。_Func
套用至這個範圍內的每個項目的使用者定義函式物件。
傳回值
函式物件的複本，然後再套用到所有在這個範圍之後的項目。
備註
這個演算法 for_each 非常有彈性，允許每個項目所做的修改在範圍內的不同，使用者指定的模式。 Templatized 函式可能會重複使用以修改過的格式傳遞不同的參數。 使用者定義的函式可能會累積在演算法可能會在處理完所有之後會傳回範圍中項目的內部狀態中的資訊。
這個範圍的參考必須是有效的，任何指標必須 dereferenceable，而且，序列中，最後一個位置必須是可取得的開頭會增加。
複雜度是線性與最多 (_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
標題: <algorithm>
命名空間: std