Re: Fast way to read string one char at a time

Hi,



The foreach loop will be slower in the case that you provide as it has a
much greater overhead for what your trying to achieve. If however, your
array/collection contained objects (just for arguments sake) and you were
required to do some additional processing on the object. The foreach loop
would start improving the performance (as well as maintainability by other
developers) as the variable would contain a reference to the actual object
allowing you to work on it directly. The for loop on the other hand would
require you to constantly reference an offset into the collection each time
you reference the object to modify a property or call a method.



You could reduce this overhead in the for loop for this example by having a
variable of the correct type and setting this in the first line of the for
statement. This will close the gape of the timings. There are still some
additional things that the foreach stament does to improve the stability of
your code that you would not be doing in the for loop.



The foreach will do the following:



First of all it extracts the IEnumerator interface from the collection using
GetEnumerator(). Then enters a while loop for the IEnumerator calling
MoveNext(). This will then typecast the current enumerator (Current() ) to
the Type specified by the variable then execute all your code.



This block is then wrapped in a try.finally block to ensure if anything goes
wrong it can free up the Enumerator interface if it implements the
IDisposable interface.

One thing you have to consider is the performance gain against the
maintainability as mentioned in the other posts. It's one thing to have
really optimised code but the price you pay comes when you or some one else
has to maintain it or modify it some months/years down the line. Having said
that a for loop is a basic operation that developers should have no problem
understanding. Are we talking about milliseconds increase in performance for
a cost of 30min + development time 4 months down the line trying to work out
how to modify it.

- Mike

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"Cosmin Prund" <cosminREMOVE@xxxxxxxxxxxxxxxxxxx> wrote in message
news:uXrtQsp6FHA.3276@xxxxxxxxxxxxxxxxxxxxxxx
> I'm trying to write a parser for a Interbase stored procedure and I want
> to identify the fastest way to go through a string one char at a time.
>
> As I'm really new to both c# and dotNet, I thought I'll share my findings
> and ask for comments:
>
> I found 4 different methods of going over the string one char at a time,
> and my results seem somewhat unexpected!
>
> [Method 1 - read directly from string - 100% timing]
> for (int i=0;i<str_len;i++) c = TestString[i]
>
>
> [Method 2 - read using StringBuilder - 200% timing]
> for (int i=0;i<str_len;i++) c = TestBuilder[i]
>
> [Method 3 - read using an CharEnumerator - 512% timing]
> ch.Reset();
> while (ch.MoveNext()) c = ch.Current;
>
>
> [Method 4 - read using a foreach loop - 170% timing]
> foreach (char c2 in TestString) c = c2
>
> After doing all those tests I ended up with lots of questions:
> 1) Why is the "foreach" loop slower then the "for" loop?
> 2) Why is the CharEnumerator so slow? Am I using this class properly?
> 3) Is my test method fair? (see attachment for my code)
>
>


.

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