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Duplicate Files Finder

, 15 Dec 2008
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A utility to find any duplicate file in your hard drives using MD5 hashing.


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Once a year, I do that terrific job of cleaning files I created or downloaded on my drives. The last time I tried to do it, it was such a fastidious task that I thought of doing that thing semi-automatically. I needed some free utility that could find duplicate files, but I found none that corresponded to my needs. I decided to write one.


The CRC calculation method is available here. I use the MD5 hashing provided by the standard libraries. I added an event to the MD5 computing method so as to get a hashing progression, it is a thread that reads the stream position while the MD5 computing method is reading the same stream.

Using the code

The utility uses two main classes, DirectoryCrawler and Comparers. The use is obvious Smile | :) Please notice that instead of iterating through a list list.count X list.count times, DuplicateFinder uses a Hashtable that contains the pair <size,count>. Once populated, all files with count =1 will be removed: (Very much faster!!!!)

int len = filesToCompare.Length;
List<long> alIdx = new List<long>();
System.Collections.Hashtable HLengths = new System.Collections.Hashtable();
foreach (FileInfo fileInfo in filesToCompare)
    if (!HLengths.Contains(fileInfo.Length))
        HLengths.Add(fileInfo.Length, 1);
        HLengths[fileInfo.Length] = (int)HLengths[fileInfo.Length] + 1;
foreach (DictionaryEntry hash in HLengths)
    if ((int)hash.Value == 1)
        setText(stsMain, string.Format("Will remove File with size {0}", hash.Key));
FileInfo[] fiZ = new FileInfo[len - alIdx.Count];
int j = 0;
for (int i = 0; i < len; i++)
    if (!alIdx.Contains(filesToCompare[i].Length))
        fiZ[j++] = filesToCompare[i];
return fiZ;

Points of interest

  • (Done) Optimizes file moving, UI may be unresponsive while moving big files Frown | :(
  • (Useless, my MD5 is better ^_^) Add options to choose between CRC32 and MD5 hashing.
  • Maybe use an XML configuration file. At this time, moving duplicate files to D:\DuplicateFiles (which is hard coded, viva Microsoft!) and skipping that folder during scanning is sufficient to me.
  • Don't forget that your posts make POIs.
  • (Done): Code an event enabled MD5 hashing class that would report hashing progression, imagine hashing a 10 GB file!


  • v0.2
    • Optimized duplicates retrieving (duplicate sizes and duplicate hashes).
    • Added Move to Recycle Bin.
    • Added file size criteria.
    • Files to delete info updated for every check/uncheck in listview.
    • Added colors and fonts to UI.
    • Debug enabled sources (#if DEBUG synchronous #else threaded).
    • Added List<Fileinfo> and List<string[]> instead of using array lists.
    • MD5 hashing is used instead of CRC32 (supercat9).
    • Added Skip Source Folder option.
    • Added Drop SubFolder.
    • Some optimizations...
  • v0.1
    • First time publishing. Waiting for bug reports Smile | :)


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


About the Author

Chief Technology Officer
Morocco Morocco
in his studies, erratum discovered c/c++.he appreciated it.
when he met oracle products, in his job, he fell in love.
he uses c# .net & ms sql.
he created a "f.r.i.e.n.d.s" like soap movie, melting all of the above.
went back in the university.
after he took courses of artificial vision & imagery, he finished his studies with a successful license plate recognition project.

Comments and Discussions

GeneralRe: Hardcoded path causes RTE PinmembereRRaTuM15-Dec-08 3:15 
Questionthread exception ! any solution?? PinmemberMember 551477514-Dec-08 10:40 
AnswerRe: thread exception ! any solution?? PinmembereRRaTuM15-Dec-08 3:31 
GeneralI like it Pinmember=Xc@libur=12-Nov-08 17:12 
GeneralRe: I like it PinmembereRRaTuM17-Nov-08 1:52 
GeneralDuplicate FIle Name finder Pinmemberpyrodood9-Sep-08 5:17 
AnswerRe: Duplicate FIle Name finder PinmembereRRaTuM15-Sep-08 16:25 
GeneralRe: Duplicate FIle Name finder [modified] Pinmemberpyrodood16-Sep-08 4:43 
Yes that is a solution. However with currently around 8000 files, and the need to check for duplicate names on a daily basis the amount of time involved as well as the high possibility for human error on such a scale proves this solution not viable in my circumstances. Thanks for the thought though.
PS. I've attempted another solution.
Command line I CD to the directory. Use:
DIR /S >1.txt
the /S lists files in the subdirectories.
the >1.txt outputs the returned lines into a text file named 1
Then I imported the file into excel, sort by filename then compare with a logical function if the one is equal to the one underneath it. Then sort by the logic return column and I have a list of duplicate name files.
One problem however, each line does not contain the location of each file, so I have a list but not sure what directories they are in, I can run a search for them.
I thought it would an easy option to add into the program being that it already creates and compares the files the directory and sub-directories.
modified on Tuesday, September 16, 2008 11:16 AM

GeneralRe: Duplicate FIle Name finder Pinmembersupercat915-Dec-08 6:29 
GeneralRe: Duplicate FIle Name finder Pinmemberpyrodood15-Dec-08 7:18 
GeneralGreat article Pinmemberfinal_zero1-Sep-08 9:09 
AnswerRe: Great article PinmembereRRaTuM15-Sep-08 16:34 
GeneralRe: Great article Pinmemberfinal_zero19-Sep-08 9:01 
GeneralRe: Great article PinmembereRRaTuM22-Sep-08 4:55 
QuestionCaching? PinmemberGregSawin1-Sep-08 7:35 
AnswerRe: Caching? PinmembereRRaTuM15-Sep-08 16:42 
GeneralRe: Caching? PinmemberPedro Barreto2-Oct-08 7:10 
AnswerCompute MD5 for everything? Pinmembersupercat915-Dec-08 12:20 
GeneralRe: Compute MD5 for everything? PinmembereRRaTuM23-Dec-08 3:47 

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