Create c# object array of undefined length?

Question

I would like to create an object array in C# of undefined length and then populate the array in a loop like so...

    string[] splitWords = message.Split(new Char[] { ' ' });

    Word[] words = new Word[];
    int wordcount = 0;
    foreach (string word in splitWords)
    {
        if (word == "") continue;
        words[wordcount] = new Word(word);
        wordcount++;
    }

However, I get the error... "Array creation must have array size or array initializer"

I'm doing a lot more logic in the foreach loop that I've left out for brevity.

Need you use an array? Doing this sort of thing with a List is often a lot easier - and can be more performant (in my experience anyway). — Bevan
– Bevan, Commented Jun 21, 2009 at 0:51

jasonh · Accepted Answer · 2009-06-21 00:43:45Z

51

What you want to do is create:

List<Word> words = new List<Word>();

and then:

words.Add(new Word(word));

And finally when the loop is done if you need an array:

words.ToArray();

answered Jun 21, 2009 at 0:43

jasonh

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Comments

JaredPar · Accepted Answer · 2009-06-21 00:44:06Z

10

If you're using C# 3.5, you can just do the following.

var words = message
  .Split(new char[]{' '}) 
  .Where(x => x != "")
  .Select(x => new Word(x))
  .ToArray();

answered Jun 21, 2009 at 0:44

JaredPar

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2 Comments

Jonathan Rupp Over a year ago

If there's not a LINQ solution to your problem, you're not trying hard enough :) Nice one.

statenjason Over a year ago

Good stuff. A note, using StringSplitOptions.RemoveEmptyEntries as your second Split() parameter would eliminate the Where() call. Although it's longer, it saves another loop through the string array.

statenjason · Accepted Answer · 2009-06-21 00:44:04Z

7

You can't create an array of undefined length. This is where you'd use a generic List.

List<Word> words = new List<Word>();

answered Jun 21, 2009 at 0:44

statenjason

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Comments

Talljoe · Accepted Answer · 2009-06-21 03:05:16Z

1

A friendly note, you can pass option to split to ignore empty entries. Assuming no other logic to prune out entries you can preinitialize your array like so:

string[] splitWords = message.Split(new Char[] {' '},
  StringSplitOptions.RemoveEmptyEntries);
Word[] words = new Word[splitWords.Length];

answered Jun 21, 2009 at 3:05

Talljoe

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1 Comment

Lyndal Over a year ago

Thanks, I did this based on another comment to an answer. Thanks, I had not yet discovered this option.

David Campbell · Accepted Answer · 2021-07-29 04:39:31Z

1

You can define a new list and convert to array...

var words = new List<Word>().ToArray();

edited Jul 29, 2021 at 4:39

answered Jul 29, 2021 at 4:31

David Campbell

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Comments

David.Chu.ca · Accepted Answer · 2009-06-21 00:49:08Z

0

Actually you may use list to populate your words first and then convert it easily to array like this:

string[] splitWords = message.Split(new Char[] { ' ' });

List<Word> words = new List<Word>();
int wordcount = 0;
foreach (string word in splitWords)
{
    if (word == "") continue;
    words.add(new Word(word));
    //wordcount++;
}

wordcount = words.count;
return words.ToArray();

answered Jun 21, 2009 at 0:49

David.Chu.ca

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Comments

Nikola K. · Accepted Answer · 2012-10-20 14:09:14Z

0

I'm wondering why can't we just use a string variable (say x), initialize it and retrieve comma separated data in it and later use string[] variable (say y[]) and initialize it equal to x.Split(',') without having to initialize a blank array like follows:

string x = string.Empty;
string msg = "hi,how,r,u,xyz";

void Page_Load(object sender, EventArgs e)
     x = msg;
     string[] y = msg.Split(',');

I think this should work as needed but I didn't try running this so I am not sure. If someone thinks that my solution is wrong, please correct me.

edited Oct 20, 2012 at 14:09

Nikola K.

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answered May 30, 2012 at 9:44

Aaaaa

1

Comments

Lyndal · Accepted Answer · 2009-06-21 00:45:50Z

-2

I solved it by using an ArrayList and then casting it to the object array after iterating...

    string[] splitWords = message.Split(new Char[] {' '});
    ArrayList wordList = new ArrayList();
    int wordcount = 0;
    foreach (string word in splitWords)
{
        if (word == "") continue;
        Word newWord = new Word(word);
        wordList.Add(newWord);
        wordcount++;
}
    Word[] words = (Word[])wordList.ToArray(typeof(Word));

I've heard the whole "create question/answer just to document it for others" is acceptable. Plus I'd like to hear if there are better suggestions. Thanks.

answered Jun 21, 2009 at 0:45

Lyndal

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2 Comments

Jonathan Rupp Over a year ago

The other answers (ie. List<Word>) is generlaly considered better, as the ToArray() is less code, and it's type-safe (you can't accidentally put non-Words in it.

Lyndal Over a year ago

Great answer of using a generic List... not sure why I didn't think of that first. Thanks! Also, I guess putting my first guess as an "answer" was not such a good idea considering the down votes and ding to my rep! ha

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