在初始化方面比较C＃中的List和C ++中的vector

Question

In C++, one can initialize a vector as

vector<int> nums1 (100, 4); // 100 integers with value 4

In additions, there is something like

vector<int> nums2 (nums1.begin() + 5, nums1.end() - 20);

Is there something similar in C# for List?

Answer 1

First one goes this:

var result = Enumerable.Repeat(4, 100);

Second one (I´m not familiar with C++) would be this ( I suppose it means something like take elements from the fith until the 20th from the end):

var result2 = result.Skip(5).Take(75);

Be aware that both result and result2 are just iterators and thus are lazily evaluated. Calling ToList or ToArray will actually materialize the collection by executing the query.

Answer 2

You can do this like this by List .

using System.Collections.Generic;
List<int> nums1 = new List<int>(Enumerable.Repeat(4,100)); //100 elements each with value 4
List<int> nums2 = new List<int>(nums1.Skip(5).Take(75)); // skip first 5 and take 75 elements