string array & arraylist

Here are the conversion routines between ArrayList, array of strings and List:

string[] array = new string[1000];
ArrayList al = new ArrayList();
al.AddRange(array);

array = new string[al.Count];

int pos = 0;
foreach (object o in al)
array[pos++] = (string)o;

List l = new List();
l.AddRange(array);
array = l.ToArray();

List under the hood implements ArrayList, so you better use that class. Then you can use its ToArray method to convert it to array.

Difference between array and list is this. Array is a structure consisting of successive memory locations. List is dispersed in memory and consists of many arrays (if list is long). Main consequence is that you cannot add elements to array without reallocating complete array and without copying its complete contents (in general case). In particular case you can use Array.Resize() method to resize the array and that method might get lucky enough to just extend (or shrink, which always succeeds) the array in-place - something similar to C realloc function.

On the contrary, you can always insert and remove items from the List and that is pretty fast because List would reallocate either nothing or only a fragment of memory it uses.

Zoran

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Zoran Horvat15y ago
Here are the conversion routines between ArrayList, array of strings and List:

string[] array = new string[1000];
ArrayList al = new ArrayList();
al.AddRange(array);

array = new string[al.Count];

int pos = 0;
foreach (object o in al)
array[pos++] = (string)o;

List l = new List();
l.AddRange(array);
array = l.ToArray();

List under the hood implements ArrayList, so you better use that class. Then you can use its ToArray method to convert it to array.

Difference between array and list is this. Array is a structure consisting of successive memory locations. List is dispersed in memory and consists of many arrays (if list is long). Main consequence is that you cannot add elements to array without reallocating complete array and without copying its complete contents (in general case). In particular case you can use Array.Resize() method to resize the array and that method might get lucky enough to just extend (or shrink, which always succeeds) the array in-place - something similar to C realloc function.

On the contrary, you can always insert and remove items from the List and that is pretty fast because List would reallocate either nothing or only a fragment of memory it uses.

Zoran
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