std::for_each的标准调用方式为：

template<class InputIt, class UnaryFunc>
constexpr UnaryFunc for_each(InputIt first, InputIt last, UnaryFunc f)
{
    for (; first != last; ++first)
        f(*first);
 
    return f; // implicit move since C++11
}

前两个参数分别表示遍历容器迭代器的开始和结束位置，而第三个参数是针对每个遍历成员的调用函数f，当然调用函数f也可以通过lambda调用来实现，下面通过实例来说明：

#include <vector>
#include <algorithm>
#include <iostream>
 
struct Sum {
    Sum() { sum = 0; }
    void operator()(int n) { sum += n; }
 
    int sum;
};
struct student {
    int age;
    int num;
};
int main()
{
    std::vector<int> nums{3, 4, 2, 9, 15, 267};
 
    std::cout << "before: ";
    for (auto n : nums) {
        std::cout << n << " ";
    }
    std::cout << '\n';
 
    std::for_each(nums.begin(), nums.end(), [](int &n){ n++; });
    Sum s = std::for_each(nums.begin(), nums.end(), Sum());
 
    std::cout << "after:  ";
    for (auto n : nums) {
        std::cout << n << " ";
    }
    std::cout << std::endl;
    int age_sum = 0, num_sum = 0;
    std::vector<student> stus = {{1,2},{2,3},{3,4},{4,5}};
    std::for_each(stus.begin(), stus.end(), [&](student& stu) {
        age_sum += stu.age;
        num_sum += stu.num;
    });
    std::cout << "age sum is " << age_sum << std::endl;
    std::cout << "num sum is " << num_sum << std::endl;
}

输出结果：

before: 3 4 2 9 15 267
after: 4 5 3 10 16 268
age sum is 10
num sum is 14

比较容易理解，需要注意的就是函数调用传入的是每个迭代器的成员，故函数参数类型要与之对应。