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\n", iItem);
}

void main()
{
    int iArray[] = {,,,,};
    vector<int> vecInt(iArray, iArray+sizeof(iArray)/sizeof(iArray[]));
    //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\n");
    else
        printf("FUNC2 != Show\n");

    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+;
 }  

 void main()
 {
     vector<int> vecIntA;
     vecIntA.push_back();
     vecIntA.push_back();
     vecIntA.push_back();
     vecIntA.push_back();
     vecIntA.push_back();

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

     int iIdx = ;
     vector<int>::iterator it = vecIntA.begin();
     while (it != vecIntA.end())
     {
         printf("[%02d] ==> %d\n", 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(), v3();
    vector <int>::iterator Iter1, Iter2 , Iter3;

    // Constructing vector v1
    int i;
    for ( i = - ; i <=  ; 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> (  ) );
    cout << "The elements of the vector v1 multiplied by 2 in place gives:"
         << "\n 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> (  ) );

    cout << "Multiplying the elements of the vector v1mod\n "
         <<  "by the factor 5 & copying to v2 gives:\n 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> (  ) );

    cout << "Multiplying elements of the vectors v1mod and v2 pairwise "
         <<  "gives:\n 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