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：