向量中的C ++乘法元素 [英] C++ Multiplying elements in a vector

问题描述

我一直在寻找一种更理想的解决方案，但似乎找不到。

I have been looking for a more optimal solution to the following and I cannot seem to find one.

假设我有一个向量：

std :: vector< double> vars = {1,2,3}

我想执行 1 * 2 * 3 我知道我可以执行以下操作：

I want to perform 1 * 2 * 3 I know that I can do the following:

int multi = 1;

for(int i = 0; (i < vars.size()-1); i++)
{
    multi *= vars[i];
}

但是，还有更多的 C ++ 11方法可以做到这一点？我真的很想使用 lambda 来做到这一点，这样我就可以计算向量的乘积（乘积），而无需在类中添加另一个函数，我宁愿将其计算出来

But, is there a more "C++11" way to do this? I really wanted to do this using lambda and so that I can calculate the multiply (product) of the vector without having another function inside the class, I'd rather have it calculated inside the function.

推荐答案

是的，像往常一样，有一种算法（尽管该算法在中; numeric> ）， std :: accumulate （实时示例）：

Yes, as usual, there is an algorithm (though this one's in <numeric>), std::accumulate (live example):

using std::begin;
using std::end;
auto multi = std::accumulate(begin(vars), end(vars), 1, std::multiplies<double>());

std :: multiplies 在< functional> 也是如此。默认情况下， std :: accumulate 使用 std :: plus ，这将为 operator（）。 std :: multiplies 是代替它们的函子。

std::multiplies is in <functional>, too. By default, std::accumulate uses std::plus, which adds two values given to operator(). std::multiplies is a functor that multiplies them instead.

在C ++ 14中，您可以替换 std :: multiplies< double> 与 std :: multiplies<> ，其 operator（ ）已被模板化，并将找出类型。根据我在Eric Niebler的Ranges提案中看到的内容，以后可能看起来像 vars | accumulate（1，std :: multiplies<>（）），但要加一点盐。

In C++14, you can replace std::multiplies<double> with std::multiplies<>, whose operator() is templated and will figure out the type. Based on what I've seen with Eric Niebler's Ranges proposal, it could possibly later look like vars | accumulate(1, std::multiplies<>()), but take that with a grain of salt.

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