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Posted 11 Aug 2008

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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File deleted


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 :) 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 :(.
  • (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 :)


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.

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Comments and Discussions

GeneralRe: Hardcoded path causes RTE Pin
eRRaTuM15-Dec-08 3:15
membereRRaTuM15-Dec-08 3:15 
Questionthread exception ! any solution?? Pin
Member 551477514-Dec-08 10:40
memberMember 551477514-Dec-08 10:40 
AnswerRe: thread exception ! any solution?? Pin
eRRaTuM15-Dec-08 3:31
membereRRaTuM15-Dec-08 3:31 
GeneralI like it Pin
=Xc@libur=12-Nov-08 17:12
member=Xc@libur=12-Nov-08 17:12 
Its just what i need - i had almost finished my own project of exactly the same thing when i found this! I assume you went down a similar path to me - i was looking for a simple, free duplicate image program and they all A) REALLY sucked, B) cost ridiculous amounts of money and C) had obvious missing features. This simple program of yours does more than any of them and its open source Smile | :)

It is quite well architected - only comment i have after very quickly skimming the code is some of it seems a bit overly complex - like you seem to have implemented your own directory recursion, rather than using Directory.GetFiles() which supports this automatically!?? Also you use a lot of FileInfo and DirectoryInfo objects which are more expensive than just using the string paths when you dont seem to make any other use of the Info classes. Perhaps you did and i just missed it in my quick scan.

In any case, great job i like it a lot
GeneralRe: I like it Pin
eRRaTuM17-Nov-08 1:52
membereRRaTuM17-Nov-08 1:52 
GeneralDuplicate FIle Name finder Pin
pyrodood9-Sep-08 5:17
memberpyrodood9-Sep-08 5:17 
AnswerRe: Duplicate FIle Name finder Pin
eRRaTuM15-Sep-08 16:25
membereRRaTuM15-Sep-08 16:25 
GeneralRe: Duplicate FIle Name finder [modified] Pin
pyrodood16-Sep-08 4:43
memberpyrodood16-Sep-08 4:43 
GeneralRe: Duplicate FIle Name finder Pin
supercat915-Dec-08 6:29
membersupercat915-Dec-08 6:29 
GeneralRe: Duplicate FIle Name finder Pin
pyrodood15-Dec-08 7:18
memberpyrodood15-Dec-08 7:18 

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