[英]How to accumulate using a Lambda function in C++?
I'm trying to accumulate the numbers in a vector using a multiplication lambda.我正在尝试使用乘法 lambda 来累积向量中的数字。
What is my error?我的错误是什么? I get 1 as the result, instead of 24 (= 1 2 3*4).结果我得到 1,而不是 24 (= 1 2 3*4)。 My approach is as follows:我的方法如下:
std::function<float(float a, int x)> func;
std::vector<int> m{ 1, 2, 3, 4 }; // <-- Multiply: 1*2*3*4 = 24
float accumulation = 1.0f;
func = [&accumulation, &m](float a, int i) {
accumulation = a * *m.begin()++;
return accumulation;
};
accumulation = accumulate(m.cbegin(), m.cend(), accumulation, func);
The idiomatic way would be:惯用的方法是:
auto accumulation = std::accumulate(m.begin(), m.end(), 1, std::multiplies{});
Your func
does a lot of odd stuff and I have no idea what you hope for with accumulation = a * *m.begin()++;
你的func
做了很多奇怪的事情,我不知道你希望用accumulation = a * *m.begin()++;
or why you leave i
unused.或者你为什么不使用i
。 This would be more like it:这更像是:
auto func = [](int lhs, int rhs) { return lhs * rhs; };
auto accumulation = std::accumulate(m.begin(), m.end(), 1, func);
Or if you want to do it with float
s:或者,如果您想使用float
s:
auto func = [](float lhs, float rhs) { return lhs * rhs; };
auto accumulation = accumulate(m.cbegin(), m.cend(), 1.f, func);
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