在C ++中创建列表列表 [英] Creating list of lists in c++

问题描述

在C ++中，推荐的创建特定大小列表的方法是什么，其中列表的每个元素都是3个元素的列表?

In C++, what is the recommended way of creating a list of a certain size, where each element of the list is a list of 3 elements?

为澄清起见，在Python中我要尝试做的类比如下:

To clarify, the analogy in Python for what I'm trying to do would go as follows:

最简单:

n = 10
ls = [[0,0,0] for i in range(n)]

和也已经初始化，我可以访问元素(例如ls[0][0])，甚至可以修改它们(ls[0][0]=2)，完美！

Already initialised as well and I can access elements (e.g. ls[0][0]) and even modify them (ls[0][0]=2), perfect!

或使用numpy

import numpy as np
n  = 10 #number of elements
ls = np.empty((n,0)).tolist()

，然后将每个3个值附加到每个元素(这里是列表).

and then to each element (here a list), we'd append our 3 values.

现在我了解在C ++中，一个开始的区别是要专门定义内部列表应该包含的变量的类型.但是vector不是c ++中的变量类型，对吗?就像这样:

Now I understand in C++, one starting difference would be to specifically define the type of variables the inner-lists are supposed to contain. But vector is not a variable type in c++ right? As in something along the lines of:

int n = 4;
vector<vector> ls(4);
for(int i=0; i<n; i++) {
    ls[i] = {0,0,0};
}

会错的.此外，如果我改用vector<int> ls;，则无法为每个元素分配列表.

would be wrong. Moreover, if I try instead vector<int> ls; then I cannot assign lists to each element.

问题:

• 有没有办法在C ++中使用vector使htis工作?
• 或者，有没有更简单的方法可以做到这一点?

• Is there a way to make htis work using vector in C++?
• Alternatively, are there simpler ways of going about this?

推荐答案

我能想到的最接近Python代码的是:

The closest to the Python code that I can think of is:

std::vector<std::vector<int>> ls(10, std::vector<int>(3));

如果在编译时知道大小，则也可以使用std::array.

If the sizes are known at compile time, you may also use std::array.

std::array<std::array<int, 3>, 10> ls;

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