In .NET, which loop runs faster, 'for' or 'foreach'?


In C#/VB.NET/.NET, which loop runs faster, for or foreach?

Ever since I read that a for loop works faster than a foreach loop a long time ago I assumed it stood true for all collections, generic collections, all arrays, etc.

I scoured Google and found a few articles, but most of them are inconclusive (read comments on the articles) and open ended.

What would be ideal is to have each scenario listed and the best solution for the same.

For example (just an example of how it should be):

  1. for iterating an array of 1000+ strings - for is better than foreach
  2. for iterating over IList (non generic) strings - foreach is better than for

A few references found on the web for the same:

  1. Original grand old article by Emmanuel Schanzer
  2. CodeProject FOREACH Vs. FOR
  3. Blog - To foreach or not to foreach, that is the question
  4. ASP.NET forum - NET 1.1 C# for vs foreach


Apart from the readability aspect of it, I am really interested in facts and figures. There are applications where the last mile of performance optimization squeezed do matter.

6/13/2012 5:30:32 PM

Accepted Answer

Patrick Smacchia blogged about this last month, with the following conclusions:

  • for loops on List are a bit more than 2 times cheaper than foreach loops on List.
  • Looping on array is around 2 times cheaper than looping on List.
  • As a consequence, looping on array using for is 5 times cheaper than looping on List using foreach (which I believe, is what we all do).
12/13/2008 8:19:54 PM

Exper Answer

It will always be close. For an array, sometimes for is slightly quicker, but foreach is more expressive, and offers LINQ, etc. In general, stick with foreach.

Additionally, foreach may be optimised in some scenarios. For example, a linked list might be terrible by indexer, but it might be quick by foreach. Actually, the standard LinkedList<T> doesn't even offer an indexer for this reason.

6/13/2012 5:46:25 PM

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