Click here to Skip to main content
13,597,589 members
Click here to Skip to main content
Add your own
alternative version

Stats

3.1K views
6 bookmarked
Posted 25 May 2018
Licenced CPOL

IEqualityComparer<FileInfo> using MD5 Hash

, 28 May 2018
Rate this:
Please Sign up or sign in to vote.
The presented code snippet compares two given files using the IEqualityComparer.

Introduction

The presented code snippet compares two given files using the IEqualityComparer.

The comparison does the following:

- Use the FileInfo's equality operator (==) to try to determine whether these are the same instances of the FileInfo class
- If one of the objects is null, they can't represent the same files, thus false is returned
- If the file path is for both objects the same, true is returned since the file must be the same
- If the file sizes differ, the files can't be the same either thus false is returned
- And at the end we resort to comparing the MD5 hash of both files.

Please keep in mind that MD5 hashing is an expensive operation, which is not suitable for comparing a lot of files or large files. The code presented here was initally intended to be used within an integration test. If you need to compare a lot of files (or very large ones) you may resort to your own implementation - You may want to start by reading this stackoverflow discussion, though.

Background

Please keep in mind that this implementation reads the file contents into the memory to create the MD5 for each file. If you're trying to compare very large files, this may slow down your application considerably.

The code

/// <summary>
/// An <see cref="IEqualityComparer{T}"/> for files using <see cref="FileInfo"/>
/// </summary>
public class FileMd5EqualityComparer : IEqualityComparer<FileInfo>
{
    /// <summary>
    /// See <see cref="IEqualityComparer{T}.Equals(T, T)"/>
    /// </summary>
    public bool Equals(FileInfo x, FileInfo y)
    {
        // Use basic comparison
        if(x == y)
        {
            return true;
        }

        // if one of both parameters is null, they can't be
        // the same - Except both are null, but this case is
        // handled above.
        if(x == null || y == null)
        {
            return false;
        }

        // If both file paths are the same, the
        // files must be the same.
        if(x.FullName == y.FullName)
        {
            return true;
        }

        // The files can't be equal if they don't
        // have the same size
        if(x.Length != y.Length)
        {
            return false;
        }

        // At last, compare the MD5 of the files.
        var md5X = GetMd5(x.FullName);
        var md5Y = GetMd5(y.FullName);

        return md5X == md5Y;
    }

    /// <summary>
    /// See <see cref="IEqualityComparer{T}.Equals(T, T)"/>
    /// </summary>
    public int GetHashCode(FileInfo obj)
    {
        return obj.GetHashCode();
    }

    /// <summary>
    /// Returns the MD5 of the file at <paramref name="filePath"/>
    /// as string
    /// </summary>
    private string GetMd5(string filePath)
    {
        using (var md5 = MD5.Create())
        {
            using (var stream = File.OpenRead(filePath))
            {
                return Encoding.Default.GetString(md5.ComputeHash(stream));
            }
        }
    }
}

History

2018-05-25 Initial version

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Share

About the Author

Marco Bertschi
Software Developer
Switzerland Switzerland
Software Developer (Swiss Federal VET Diploma), experienced with Qt C++, Arduino Boards, multiple communication technologies (the usual Webservices, TCP/IP bunch as well as serial port communication), and C# including WPF, Entity Framework and COM libraries built using the .Net Framework.
Music enthusiast, runner, part-time psychologist for friends, awesome guy and Air Force Sergeant First Class.

You may also be interested in...

Pro
Pro

Comments and Discussions

 
QuestionGetHashCode for object equality comparison Pin
Member 95112430-May-18 4:23
memberMember 95112430-May-18 4:23 
QuestionWhy determine hash... Pin
0x01AA25-May-18 12:43
professional0x01AA25-May-18 12:43 
AnswerRe: Why determine hash... Pin
Marco Bertschi28-May-18 4:19
protectorMarco Bertschi28-May-18 4:19 
Suggestionmd5 is expanciv and slow in this special case ! Pin
Peter BCKR25-May-18 2:18
memberPeter BCKR25-May-18 2:18 
GeneralRe: md5 is expanciv and slow in this special case ! Pin
Marco Bertschi28-May-18 4:18
protectorMarco Bertschi28-May-18 4:18 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

Permalink | Advertise | Privacy | Cookies | Terms of Use | Mobile
Web03-2016 | 2.8.180621.3 | Last Updated 28 May 2018
Article Copyright 2018 by Marco Bertschi
Everything else Copyright © CodeProject, 1999-2018
Layout: fixed | fluid