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Posted 11 Aug 2008

Duplicate Files Finder

, 15 Dec 2008 CPOL
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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: Missing ConsoleTestRestorer & Restorer Pin
k2ox27-Nov-10 8:06
memberk2ox27-Nov-10 8:06 
GeneralDuplicate File Finder , Name Finder , Zero Lenght etc Pin
stixoffire22-Dec-08 22:25
memberstixoffire22-Dec-08 22:25 
GeneralRe: Duplicate File Finder , Name Finder , Zero Lenght etc Pin
eRRaTuM23-Dec-08 3:37
membereRRaTuM23-Dec-08 3:37 
GeneralRe: Duplicate File Finder , Name Finder , Zero Lenght etc Pin
Booya10014-Jan-09 13:35
memberBooya10014-Jan-09 13:35 
AnswerRe: Duplicate File Finder , Name Finder , Zero Lenght etc Pin
eRRaTuM14-Jan-09 15:42
membereRRaTuM14-Jan-09 15:42 
GeneralMy vote of 5. Pin
Lion_King110922-Dec-08 18:03
memberLion_King110922-Dec-08 18:03 
GeneralRe: My vote of 5. Pin
eRRaTuM23-Dec-08 3:51
membereRRaTuM23-Dec-08 3:51 
GeneralDuplicate Files Finder. MD5 Encryption Pin
Henry Minute15-Dec-08 6:20
memberHenry Minute15-Dec-08 6:20 
Good Article! Useful tool.
As you seem to have an interest in this sort of thing, you are perhaps aware of the possibility of 'collisions' in MD5, but in case you aren't take a look at

I know so little about encryption that I can't tell if there is a possibility that this could happen for your code, it's just that I came accross the link yesterday and your article today.


Henry Minute

Never read Medical books. You could die of a misprint. - Mark Twain

GeneralRe: Duplicate Files Finder. MD5 Encryption Pin
eRRaTuM23-Dec-08 3:49
membereRRaTuM23-Dec-08 3:49 
GeneralHardcoded path causes RTE Pin
At Nel14-Dec-08 18:43
memberAt Nel14-Dec-08 18:43 
GeneralRe: Hardcoded path causes RTE Pin
eRRaTuM15-Dec-08 4:15
membereRRaTuM15-Dec-08 4:15 
Questionthread exception ! any solution?? Pin
Member 551477514-Dec-08 11:40
memberMember 551477514-Dec-08 11:40 
AnswerRe: thread exception ! any solution?? Pin
eRRaTuM15-Dec-08 4:31
membereRRaTuM15-Dec-08 4:31 
GeneralI like it Pin
=Xc@libur=12-Nov-08 18:12
member=Xc@libur=12-Nov-08 18:12 
GeneralRe: I like it Pin
eRRaTuM17-Nov-08 2:52
membereRRaTuM17-Nov-08 2:52 
GeneralDuplicate FIle Name finder Pin
pyrodood9-Sep-08 6:17
memberpyrodood9-Sep-08 6:17 
AnswerRe: Duplicate FIle Name finder Pin
eRRaTuM15-Sep-08 17:25
membereRRaTuM15-Sep-08 17:25 
GeneralRe: Duplicate FIle Name finder [modified] Pin
pyrodood16-Sep-08 5:43
memberpyrodood16-Sep-08 5:43 
GeneralRe: Duplicate FIle Name finder Pin
supercat915-Dec-08 7:29
membersupercat915-Dec-08 7:29 
GeneralRe: Duplicate FIle Name finder Pin
pyrodood15-Dec-08 8:18
memberpyrodood15-Dec-08 8:18 
GeneralGreat article Pin
final_zero1-Sep-08 10:09
memberfinal_zero1-Sep-08 10:09 
AnswerRe: Great article Pin
eRRaTuM15-Sep-08 17:34
membereRRaTuM15-Sep-08 17:34 
GeneralRe: Great article Pin
final_zero19-Sep-08 10:01
memberfinal_zero19-Sep-08 10:01 
GeneralRe: Great article Pin
eRRaTuM22-Sep-08 5:55
membereRRaTuM22-Sep-08 5:55 
QuestionCaching? Pin
GregSawin1-Sep-08 8:35
memberGregSawin1-Sep-08 8:35 

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