cb35a_c++_STL_算法_for

cb35a_c++_STL_算法_for_each

for_each(b,e,p)
使用for_each()算法遍历数据
使用for_each()和函数对象修改数据
使用for_each()的返回值

//转换函数operator double()
//参考：https://www.cnblogs.com/txwtech/p/12115391.html
//static_cast<double>强制类型转换：

MeanValue mv=for_each(ivec.begin(), ivec.end(), MeanValue());//for_each的返回值给到mv,mv里面保留了 num与sum的结果。
cout << "平均值：" << mv.value() << endl;

double result= for_each(ivec.begin(), ivec.end(), MeanValue());
//for_each的返回值给到result,result定义为了doubule,它自动调用类型转换函数operator double()
cout << "平均值2：" << result << endl;

 1 /*cb35a_c++_STL_算法_for_each
 2 
 3 for_each(b,e,p)
 4 使用for_each()算法遍历数据
 5 使用for_each()和函数对象修改数据
 6 使用for_each()的返回值
 7 
 8 //转换函数operator double()
 9     //参考：https://www.cnblogs.com/txwtech/p/12115391.html
10     //static_cast<double>强制类型转换：
11 
12     MeanValue mv=for_each(ivec.begin(), ivec.end(), MeanValue());//for_each的返回值给到mv,mv里面保留了 num与sum的结果。
13     cout << "平均值：" << mv.value() << endl;
14 
15     double result= for_each(ivec.begin(), ivec.end(), MeanValue());
16     //for_each的返回值给到result,result定义为了doubule,它自动调用类型转换函数operator double()
17     cout << "平均值2：" << result << endl;
18 
19 */
20 
21 #include <iostream>
22 #include <algorithm>
23 #include <vector>
24 using namespace std;
25 
26 void print(int elem)
27 {
28     cout << elem << ' ';
29 }
30 template<class T>
31 class AddValue
32 {
33 private:
34     T theValue;
35 public:
36     AddValue(const T& v) :theValue(v) {}
37     void operator()(T& elem) const
38     {
39         elem += theValue;
40     }
41 };
42 class MeanValue
43 {
44 private:
45     long num;
46     long sum;
47 public:
48     MeanValue() :num(0), sum(0) {}
49     void operator()(int elem)//operator就是函数对象
50     {
51         num++;
52         sum += elem;
53     }
54     double value()
55     {
56         return static_cast<double>(sum) / static_cast<double>(num);
57         //static_cast<double>强制类型转换：
58          //https://blog.csdn.net/txwtech/article/details/104148011
59     }
60 
61     //类型转换函数operator double()，double运算符重载
62     //参考：https://www.cnblogs.com/txwtech/p/12115391.html
63     operator double()
64     {
65         return static_cast<double>(sum) / static_cast<double>(num);
66     }
67 
68 };
69 
70 int main()
71 {
72     vector<int> ivec;
73     for (int i = 1; i <= 9; ++i)
74         ivec.push_back(i);
75     for_each(ivec.begin(), ivec.end(), print);
76     cout << endl;
77     for_each(ivec.begin(), ivec.end(), AddValue<int>(10));//函数对象，自动调用operator
78     for_each(ivec.begin(), ivec.end(), print);
79     cout << endl;
80     for_each(ivec.begin(), ivec.end(), AddValue<int>( *ivec.begin()));
81     for_each(ivec.begin(), ivec.end(), print);
82     cout << endl;
83      // MeanValue()是函数对象，返回也是函数对象
84     MeanValue mv=for_each(ivec.begin(), ivec.end(), MeanValue());//for_each的返回值给到mv,mv里面保留了 num与sum的结果。
85     cout << "平均值：" << mv.value() << endl;
86 
87     double result= for_each(ivec.begin(), ivec.end(), MeanValue()); 
88     //for_each的返回值给到result,result定义为了doubule,它自动调用类型转换函数operator double()
89     cout << "平均值2：" << result << endl;
90 
91 
92     return 0;
93 }

欢迎讨论，相互学习。 txwtech@163.com