File Equals: Compare Files
This page was last reviewed on Jan 8, 2024.
Dot Net Perls
File equals. How can we determine if 2 files are equal? We can compare lengths, dates created and modified. But this is not always enough.
Equal contents. There is no way to know if the contents are the same unless we test them. We demonstrate a method that compares 2 files for equality.
Example. The simplest way to check 2 files for equal contents is to use File.ReadAllBytes on each file. Then we must compare the result arrays.
And If the arrays have the same length, each byte must be compared. If the arrays have different lengths, we know the files are not equal.
Note The output of this program will depend on the contents of the two files. Please change the paths in Main().
using System; using System.IO; class Program { static bool FileEquals(string path1, string path2) { byte[] file1 = File.ReadAllBytes(path1); byte[] file2 = File.ReadAllBytes(path2); if (file1.Length == file2.Length) { for (int i = 0; i < file1.Length; i++) { if (file1[i] != file2[i]) { return false; } } return true; } return false; } static void Main() { bool a = FileEquals("C:\\stage\\htmlmeta", "C:\\stage\\htmlmeta-aspnet"); bool b = FileEquals("C:\\stage\\htmllink", "C:\\stage\\htmlmeta-aspnet"); Console.WriteLine(a); Console.WriteLine(b); } }
True False
FileInfo note. If the common case in your program is that the files are not equal, then using a FileInfo struct and the Length property to compare lengths first would be faster.
File Size
Usage. Suppose we are trying to update a directory of files but some files may not be different. Instead of rewriting files, we can test them for equality first.
So If they are equal, we can just do nothing. Reading in a file is a lot faster than writing out a file.
Detail In this use case, this FileEquals method can significantly improve performance.
Summary. We can guess whether two files are equal by testing their dates and lengths. But we cannot know if every single byte is equal unless we test every single byte.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Jan 8, 2024 (edit).
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