[ACCEPTED]-why foreach is faster than for loop while reading richtextbox lines-richtextbox
As Mehrdad noted, accessing the Lines property 9 takes a long time. You need to be careful 8 here - you're accessing it twice in each iteration 7 at the moment:
String s = String.Empty;
for (int i = 0; i < richTextBox.Lines.Length; i++)
{
s = richTextBox.Lines[i];
}
Even if you remove the access 6 in the body of the loop like this:
String s = String.Empty;
for (int i = 0; i < richTextBox.Lines.Length; i++)
{
}
you're 5 still accessing Lines on every iteration to see if 4 you've finished!
If you don't want to foreach, you 3 can just fetch Lines once:
string[] lines = richTextBox.Lines;
for (int i = 0; i < lines.Length; i++)
{
s = lines[i];
}
Personally I prefer 2 the foreach unless you really need the index though 1 :)
I think the Lines property is recalculated every 8 time you want to access it. Consequently, the 7 foreach method performs the calculation only once, while 6 every time your reference Lines[i] it's re-evaluating 5 the whole thing. Try caching the result 4 of Lines property and checking again:
String s = String.Empty;
var lines = richtextbox.Lines;
for(int i = 0; i < lines.Length; i++)
{
s = lines[i];
}
By the way, your 3 question makes an implicit assumption that 2 foreach is always slower than for. This is not always 1 true.
Probably because finding the next line in 7 the textbox takes time. When you use random-access 6 by indexing in the first case, it must find 5 that line from scratch. When the iteration 4 is done internally by foreach, it can retain state 3 and quickly find the next line.
This should 2 make the first case run in O(n^2) time, while 1 the second runs in O(n).
Could it be that each line is being copied 3 to a new string variable (str) on each loop? I'm 2 guissing here, but you could probably verify 1 the theory with this code
String s = String.Empty;
for (int i = 0; i < richTextBox.Lines.Length; i++)
{
string str = richTextBox.Lines[i];
s = str;
}
.NET Reflector is very useful to determine why you're seeing 3 performance you don't expect.
Give it a try 2 to look at the Lines get accessor to see what it 1 actually does each time you access it.
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