STL_算法_06_遍历算法

◆ 常用的遍历算法：

1.1、用指定函数依次对指定范围内所有元素进行迭代访问。该函数不得修改序列中的元素

functor for_each(iteratorBegin, iteratorEnd, functor对每个元素进行操作);

1.2、与for_each类似，遍历所有元素，但可对容器的元素进行修改（ transform 是变换的意思）

OutputIterator transform(InputIterator _First1,   InputIterator _Last1,  OutputIterator _Result, 一元functor对每个元素进行操作);
OutputIterator transform(InputIterator1 _First1, InputIterator1 _Last1, InputIterator2 _First2,  OutputIterator _Result, 二元functor对每个元素进行操作);

1、

1.1、第6讲 PPT.42

◆ for_each() :  用指定函数依次对指定范围内所有元素进行迭代访问。该函数不得修改序列中的元素。

ZC: 只有一种参数格式，返回值为 传入的functor 。

ZC: vs2010 测试代码：

#ifdef WIN32
#pragma warning (disable: 4786)
#endif

#include <string>
#include <vector>
#include <set>

#include <algorithm>    // 算法
#include <numeric>    // 算法
#include <functional>    // 算法

using namespace std;

typedef void (*FUNC1)(const int &_iItem);
void (*FUNC2)(const int &_iItem);

void Show(const int &iItem)
{
    //cout << iItem;
    printf("iItem : %d
", iItem);
}

void main()
{
    int iArray[] = {0,1,2,3,4};
    vector<int> vecInt(iArray, iArray+sizeof(iArray)/sizeof(iArray[0]));
    //FUNC1 = for_each(vecInt.begin(), vecInt.end(), Show); // ZC: 编译通不过
    FUNC2 = for_each(vecInt.begin(), vecInt.end(), Show);

    if (FUNC2 == Show)
        printf("FUNC2 == Show
");
    else
        printf("FUNC2 != Show
");

    system("pause");
}

ZC：控制台输出：

iItem : 0
iItem : 1
iItem : 2
iItem : 3
iItem : 4
FUNC2 == Show
请按任意键继续. . .

1.2、第6讲 PPT.42

◆ transform() :   与for_each类似，遍历所有元素，但可对容器的元素进行修改

ZC: 2种参数格式，返回值为 输出容器中 经过转换后的最后一个元素的iterator 。

ZC: VC6 测试代码：

#ifdef WIN32
#pragma warning (disable: 4786)
#endif

#include <string>
#include <vector>
#include <set>

#include <algorithm>    // 算法
#include <numeric>    // 算法
#include <functional>    // 算法

using namespace std;

int Increase (int i)  
{  
    return i+1;   
}  

void main()
{
    vector<int> vecIntA;
    vecIntA.push_back(1);
    vecIntA.push_back(3);
    vecIntA.push_back(5);
    vecIntA.push_back(7);
    vecIntA.push_back(9);

    transform(vecIntA.begin(), vecIntA.end(), vecIntA.begin(), Increase);    //vecIntA : {2,4,6,8,10}

    int iIdx = 0;
    vector<int>::iterator it = vecIntA.begin();
    while (it != vecIntA.end())
    {
        printf("[%02d] ==> %d
", iIdx, *it);
        it ++;
    }
}

ZC：控制台输出 - 1：

[00] ==> 2
[00] ==> 4
[00] ==> 6
[00] ==> 8
[00] ==> 10
Press any key to continue

ZC: vs10 测试代码：

// alg_transform.cpp
// compile with: /EHsc
#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;
      }
};

template <class Type>
class MultValue2
{
   private:
      Type Factor;   // The value to multiply by
   public:
      // Constructor initializes the value to multiply by
      MultValue2 ( const Type& _Val ) : Factor ( _Val )
      {}

      // The function call for the element to be multiplied
      int operator ( ) ( Type& elem1, Type& elem2 ) const 
      {
         return elem1*elem2 * 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 << 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:"
        << "
 v1mod = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl << 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
 "
        <<  "by the factor 5 & copying to v2 gives:
 v2 = ( " ;
   for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ )
      cout << *Iter2 << " ";
   cout << ")." << endl << endl;

   // The second version of transform used to multiply the 
   // elements of the vectors v1mod & v2 pairwise
   // ZC: 预定义的 二元functor
   //transform ( v1.begin ( ) , v1.end ( ) ,  v2.begin ( ) , v3.begin ( ) , 
   //   multiplies <int> ( ) );
   // ZC: 自定义的 二元functor
   transform ( v1.begin ( ) , v1.end ( ) ,  v2.begin ( ) , v3.begin ( ) , MultValue2<int> ( 2 ) );
   
   
   cout << "Multiplying elements of the vectors v1mod and v2 pairwise "
        <<  "gives:
 v3 = ( " ;
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )
      cout << *Iter3 << " ";
   cout << ")." << endl;

   system("pause");
}

ZC：控制台输出 - 2：

Original vector  v1 = ( -4 -3 -2 -1 0 1 2 ).

The elements of the vector v1 multiplied by 2 in place gives:
 v1mod = ( -8 -6 -4 -2 0 2 4 ).

Multiplying the elements of the vector v1mod
 by the factor 5 & copying to v2 gives:
 v2 = ( -40 -30 -20 -10 0 10 20 ).

Multiplying elements of the vectors v1mod and v2 pairwise gives:
 v3 = ( 640 360 160 40 0 40 160 ).
请按任意键继续. . .

?.?、第6讲 PPT.?

◆ 

ZC: VC6 测试代码：

ZC：控制台输出：

X