非修改性序列算法之for

for_each是algorithm头文件包含的stl算法之一。

一、for_each的使用

#include<iostream> #include<vector> #include<algorithm> using namespace std; template<typename T> int pushNum(T &vec, int first, int last) { int ret = 0; if (first > last) { ret = -1; cout << "function pushNum first > last error" << ret << endl; } while (first <= last) { vec.push_back(first); first++; } return ret; } template<typename T> void printNum(T &num) { cout << num << " "; } int main(){ vector<int> vec; pushNum(vec, 1, 10); for_each(vec.begin(), vec.end(), printNum<int>); cout << endl; system("pause"); return 0; }

输出结果：

二、for_each仿函数的用法

#include<iostream> #include<vector> #include<algorithm> using namespace std; template<typename T> int pushNum(T &vec, int first, int last) { int ret = 0; if (first > last) { ret = -1; cout << "function pushNum first > last error" << ret << endl; } while (first <= last) { vec.push_back(first); first++; } return ret; } template<typename T> class Print { private: T num; public: Print(T t) :num(t) {} void operator()(T& ele)const { ele *= num; } }; int main(){ vector<int> vec; pushNum(vec, 1, 10); for_each(vec.begin(), vec.end(), Print<int>(2)); for_each(vec.begin(), vec.end(), printNum<int>); cout << endl; system("pause"); return 0; }

输出结果：

三、for_each的返回值用法

#include<iostream> #include<vector> #include<algorithm> using namespace std; template<typename T> int pushNum(T &vec, int first, int last) { int ret = 0; if (first > last) { ret = -1; cout << "function pushNum first > last error" << ret << endl; } while (first <= last) { vec.push_back(first); first++; } return ret; } template<typename T> class SUM { private: long sum_num; public: SUM() :sum_num(0) {} void operator()(T ele) { sum_num += ele; } operator double() { return static_cast<double>(sum_num); } }; int main(){ vector<int> vec; pushNum(vec, 1, 10); double sum = for_each(vec.begin(), vec.end(), SUM<int>()); cout << sum << endl; system("pause"); return 0; }

输出结果：

这里注意一点，SUM类中必须有类型强制转换重载，具体强制转换的类型是什么视具体而定。