{"id":213,"date":"2022-03-12T14:25:18","date_gmt":"2022-03-12T14:25:18","guid":{"rendered":"https:\/\/baldsolutions.com\/?p=213"},"modified":"2022-03-12T14:37:12","modified_gmt":"2022-03-12T14:37:12","slug":"for-vs-foreach-performance-difference","status":"publish","type":"post","link":"https:\/\/baldsolutions.com\/index.php\/2022\/03\/12\/for-vs-foreach-performance-difference\/","title":{"rendered":"For vs Foreach – performance difference"},"content":{"rendered":"\n
Introduction<\/h1>\n\n\n\n
Iterating through collections is part and parcel of programming. As a C# developer you’ve probably used for<\/code> and foreach<\/code>. Both helps to iterate through a collection, but it’s worth to be aware that there are ins and outs. In this post I will show and explain performance differences between iterating through an array and a list using for<\/code> and foreach<\/code>.<\/p>\n\n\n\n
Performance<\/h1>\n\n\n\n
Let’s consider the following code snippet:<\/p>\n\n\n\n
public class CollectionsHolder\r\n{\r\n private readonly List<int> _list;\r\n private readonly int[] _array;\r\n\r\n public CollectionsHolder(int count)\r\n {\r\n _list = new List<int>(Enumerable.Range(0, count));\r\n _array = new int[count];\r\n }\r\n\r\n public void ForLoopList()\r\n {\r\n for (int i = 0; i < _list.Count; i++) { }\r\n }\r\n\r\n public void ForeachLoopList()\r\n {\r\n foreach (var item in _list) { }\r\n }\r\n\r\n public void ForLoopArray()\r\n {\r\n for (int i = 0; i < _array.Length; i++) { }\r\n }\r\n\r\n public void ForeachLoopArray()\r\n {\r\n foreach (var item in _array) { }\r\n }\r\n}<\/code><\/pre>\n\n\n\n
The CollectionsHolder<\/code> class stores two collections: _list <\/code>and _array<\/code>. There are four methods that do nothing but iterate through a particular collection – pretty useless but good enough in terms of benchmarking.<\/p>\n\n\n\n
Benchmark (1_000_000_000 elements per collection) results for these four methods stand as follows:<\/p>\n\n\n\n
<\/figure><\/div>\n\n\n\n
It turns out that foreach<\/code> iteration time is ~7 times slower than using classic for<\/code> when it comes to the list iteration. Surprisingly, foreach<\/code> iteration through the array lasts the same as using for<\/code> loop. The question is, why ForLoopList<\/code>, ForLoopArray <\/code>and ForeachLoopArray<\/code> last the same, meanwhile ForeachLoopList<\/code> lasts much longer?<\/p>\n\n\n\n
![\"\"](\"https:\/\/baldsolutions.com\/wp-content\/uploads\/2022\/03\/image.png\")
<\/figure><\/div>\n\n\n\n![\"\"](\"https:\/\/baldsolutions.com\/wp-content\/uploads\/2022\/03\/image-4.png\")
<\/figure><\/div>\n\n\n\n