Extra List<> object in memory

Question

Consider this simple code:

class Program
{
    static List<Data> listData = new List<Data>();
    static void Main(string[] args)
    {
        for (int i = 0; i < 5; i++)
        {
            Data newData = new Data();
            newData.num1 = i;
            newData.num2 = i * 5;
            listData.Add(newData);
        }
        Console.ReadLine();
    }
}

class Data
{
    public int num1 { get; set; }
    public int num2 { get; set; }
}

For some reason, when profiling memory for this code, it shows that there are 2 Data[] objects in memory (which i assume are listData objects): dotMemory 4 ss Can anyone explain why?

what is this `ConsoleApplication.Data[]` ? to count how much instance you have use `listData.Count` — AsfK, Nov 09 '14 at 14:52
@AsfK listData.Count will give me the number of Data's, not instances of listData's. — user1307346, Nov 09 '14 at 14:57

score 3 · Accepted Answer · edited May 23 '17 at 10:33

3

No, you don't have an extra List<Data> in memory, you have two Data[] arrays. Which are the underlying storage for the List<> object you created.

List<> starts out with an empty array, the first Add() call creates a Data[] array that can fit 4 elements. Which runs out on the fifth Add() call, it now creates a Data[] array that's double the size, it can store 8 elements. Your memory profiler still sees the Data[] array that's garbage, the GC hasn't run yet.

You can use the Capacity property to optimize this. Lots more details in this post.

edited May 23 '17 at 10:33

Community

1
1

answered Nov 09 '14 at 14:59

Hans Passant

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Thanks for explaining, but when i force GC - nothing is removed. – user1307346 Nov 09 '14 at 15:03
1

You'll have to ask another question, read [this post](http://stackoverflow.com/a/17131389/17034) first. – Hans Passant Nov 09 '14 at 15:15

score 2 · Answer 2 · answered Nov 09 '14 at 14:48

2

I think you can count on the garbage collector to do its job... don't worry about it (I don't have enough reputation to post this as comment)

answered Nov 09 '14 at 14:48

o.z

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Thanks but forcing GC doesn't remove it. And i would like to understand why there are 2 of them. – user1307346 Nov 09 '14 at 14:50

Extra List<> object in memory

2 Answers2