C++ std::accumulate函数用法

accumulate定义在#include中，有两种用法，一个是累加求和，另一个是自定义类型数据的处理

默认累加求和

template< class InputIt, class T >
T accumulate( InputIt first, InputIt last, T init );

自定义对数据的处理

template< class InputIt, class T, class BinaryOperation >
constexpr T accumulate( InputIt first, InputIt last, T init,
                        BinaryOperation op );

参数

first, last: 要求和的元素范围

init：和的初值

op:被使用的二元函数对象。接收当前积累值 a （初始化为 init ）和当前元素 b 的二元运算符。

例子

// accumulate example
#include <iostream>     // std::cout
#include <functional>   // std::minus
#include <numeric>      // std::accumulate

int myfunction (int x, int y) {return x+2*y;}
struct myclass {
	int operator()(int x, int y) {return x+3*y;}
} myobject;

int main () {
    int init = 100;
    int numbers[] = {10,20,30};

    std::cout << "using default accumulate: ";
    std::cout << std::accumulate(numbers,numbers+3,init);
    std::cout << '\n';

    std::cout << "using functional minus: ";
    std::cout << std::accumulate (numbers, numbers+3, init, std::minus<int>());
    std::cout << '\n';

    std::cout << "using custom function: ";
    std::cout << std::accumulate(numbers, numbers + 3, 0, [](int a, Grade b){return a + b * 2; });
    std::cout << '\n';

    std::cout << "using custom object: ";
    std::cout << std::accumulate (numbers, numbers+3, init, myobject);
    std::cout << '\n';

    return 0;
}

输出：

using default accumulate: 160
using functional minus: 40
using custom function: 120
using custom object: 280

转载自C++ Lambda表达式的基本使用