为什么 std::accumulate 函数会显示向量的错误总和<double>? [英] Why is the std::accumulate function showing the wrong sum of a vector<double>?

问题描述

考虑以下代码来添加 vector 的所有元素:

Consider the following code for adding all the elements of a vector:

#include<iostream>
#include<algorithm>
#include<numeric>
#include<vector>
using namespace std;
int main(void)
{

   std::vector<double> V;
   V.push_back(1.2);
   V.push_back(3.6);
   V.push_back(5.6);
   double sum = accumulate(V.begin(),V.end(),0);

   cout << "The sum of the elements of the vector V is " << sum << endl;
   return 0;
}

当我在 Windows 上的 Cygwin 上编译并运行它时，我在终端得到输出

When I compile this on Cygwin on Windows and run it, I get the output at the terminal as

向量V的元素之和为9

accumulate 函数似乎将所有数字四舍五入并将它们相加，这将解释答案.

The accumulate function seems to be rounding down all the numbers and adding them up, which would explain the answer.

这是 Cygwin g++ 编译器有问题，还是我对 accumulate 函数的错误解释，用于将 double 的vector 相加?

Is this something wrong with the Cygwin g++ compiler, or my misinterpretation of the accumulate function for adding up a vector of doubles?

推荐答案

std::accumulate 声明如下:

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

std::accumulate 的第二个模板参数被推导出为 int 因为 0 是 int 类型.改为传递双精度值，例如 0.0.

The second template argument to std::accumulate is deduced as int because 0 is of type int. Pass a double instead, like 0.0.

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