Unable to make arrays in a list/arraylist

Question

I need to make array in a arraylist or in a list, I used this:

List<string[]> OL = new List<string[]>();
string[] OLdata = new string[7];

OLdata[0] = .. ; OLdata[1] = .. OLdata[6] = ..
OL.Add(OLdata);

and I can access it with

    OL[0].GetValue(3) or OL[0][3] ..

again writing to OLdata and adding it in OL list, when I try to access data with

    OL[0][3] ..

I am getting the new data which was inserted in array, I am obviously expecting different values in OL[0][3] and OL[1][3] , whats the reason or any other suggestion ??

In your code you have not added a second array. To be honest with you, since I don't see a second Add statement I'd say accessing OL[1][3] this way should throw an exception. If you've just added OLdata twice, then I would have to +1 @LukeH's answer. — Joel Etherton
– Joel Etherton, Commented Nov 1, 2011 at 14:16
I think there are mistakes in your question. OL[0] = ..; OL[1] = ... should be OLdata[0] = ...; OLdata[1] = ... — codeulike
– codeulike, Commented Nov 1, 2011 at 14:17

LukeH · Accepted Answer · 2011-11-01 14:12:40Z

5

Arrays are reference types, so all you're actually doing is altering and then adding the same array object multiple times.

You should probably do something like this instead, creating and populating a new array each time:

var olData = new string[7];  // create first array
olData[0] = ...  // etc
ol.Add(olData);  // add first array

olData = new string[7];  // create second array
olData[0] = ...  // etc
ol.Add(olData);  // add second array

// ...

answered Nov 1, 2011 at 14:12

LukeH

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4 Comments

Rony Over a year ago

o yea..any solution to that ?

Josh Maag Over a year ago

@Rony the "new" on olData needs to be called every time you want a new item in the list.

Joel Etherton Over a year ago

+1 - I see in his description where he is simply adding the same object as a second element. He's probably also surprised to see his new addition appearing in OL[0] as well.

Security Hound Over a year ago

I would argue this really should not be done. It really sounds like he should make the collection a property of a class and make reference a collection of that class.

Josh Maag · Accepted Answer · 2011-11-01 14:14:36Z

1

When you add your second string array, are you creating a new string[7]?

E.G.

List<string[]> OL = new List<string[]>();
string[] OLdata = new string[7];

OL[0] = .. ; OL[1] = .. OL[6] = ..
OL.Add(OLdata);

OLdata = new string[7];

OL[0] = .. ; OL[1] = .. OL[6] = ..
OL.Add(OLdata);

answered Nov 1, 2011 at 14:14

Josh Maag

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