Databases
StackOverflow2013
Postsdbo
POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
    primarykey
    data
    text
    <p>I have a very long string (<strong>60MB</strong> in size) in which I need to find how many pairs of '&lt;' and '>' are in there.</p> <hr> <p>I have first tried my own way:</p> <pre><code> char pre = '!'; int match1 = 0; for (int j = 0; j &lt; html.Length; j++) { char c = html[j]; if (pre == '&lt;' &amp;&amp; c == '&gt;') //find a match { pre = '!'; match1++; } else if (pre == '!' &amp;&amp; c == '&lt;') pre = '&lt;'; } </code></pre> <p>The above code runs on my string for roughly <strong>1000 ms</strong>.</p> <hr> <p>Then I tried using <code>string.IndexOf</code></p> <pre><code> int match2 = 0; int index = -1; do { index = html.IndexOf('&lt;', index + 1); if (index != -1) // find a match { index = html.IndexOf('&gt;', index + 1); if (index != -1) match2++; } } while (index != -1); </code></pre> <p>The above code runs for only around <strong>150 ms</strong>. </p> <hr> <p>I am wondering what is the magic that makes <code>string.IndexOf</code> runs <strong>so fast</strong>?</p> <p>Anyone can inspire me?</p> <hr> <p><strong>Edit</strong></p> <p>Ok, according to @BrokenGlass's answer. I modified my code in the way that they don't check the pairing, instead, they check how many '&lt;' in the string.</p> <hr> <pre><code> for (int j = 0; j &lt; html.Length; j++) { char c = html[j]; if (c == '&gt;') { match1++; } } </code></pre> <p>the above code runs for around <strong>760 ms</strong>.</p> <hr> <p>Using <code>IndexOf</code></p> <pre><code> int index = -1; do { index = html.IndexOf('&lt;', index + 1); if (index != -1) { match2++; } } while (index != -1); </code></pre> <p>The above code runs for about <strong>132 ms</strong>. <strong>still very very fast.</strong> </p> <hr> <p><strong>Edit 2</strong></p> <p>After read @Jeffrey Sax comment, I realised that I was running in VS with Debug mode.</p> <p>Then I built and ran in release mode, ok, <code>IndexOf</code> is still faster, but not that faster any more.</p> <p>Here is the results:</p> <p>For the pairing count: <strong>207ms VS 144ms</strong></p> <p>For the normal one char count: <strong>141ms VS 111ms</strong>.</p> <p>My own codes' performance was really improved. </p> <hr> <p><strong>Lesson learned: when you do the benchmark stuff, do it in release mode!</strong></p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USJack
    1. USJack
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
      1. This table or related slice is empty.
      1. VTUpMod
    1. CODid you enable optimizations while testing?
      singulars
      1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
      1. USMartin Liversage
    2. COHave you taken a look at what `string.IndexOf` is doing behind the scenes?
      singulars
      1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
      1. USzimdanen
    3. CO@MartinLiversage How to enable optimizations?
      singulars
      1. POHow can C#'s string.IndexOf perform so fast, 10 times faster than ordinary for loop find?
      1. USJack
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload