• 0

[C++] Test if two files are the same?


Question

I'm not looking to test if two files are duplicates, I know you can do that by doing a byte by byte comparison, or hashing both files.

What I'm looking for is a way to test if both files are literally the same file. For example:

c:\documents and settings\bla.txt

c:\docume~1\bla.txt

When comparing the strings, those might be seen as two different files, when really they're the same file. I could convert both strings to short file names, but I'm not sure if Windows has other ways of linking files to eachother.

In brief, I need a foolproof way to test if two files are the same file or different.

Link to comment
https://www.neowin.net/forum/topic/349791-c-test-if-two-files-are-the-same/
Share on other sites

21 answers to this question

Recommended Posts

  • 0

Well i can just give you puesudo code:

Read both files and store the text inside, into two seperate strings

--> If string 1 == string 2

Do what you want to happen

You will have to check yourself, or let someone else find out how to read the files, since i haven't learned about reading files yet.

  • 0

So your question is how are you supposed to see if two files are identical without comparing contents of them!?

Btw, love your avatar - reminds me of when I was creating demos in DOS and I made effect that looked exactly as your avatar... heh..

  • 0

so let me see if i'm getting the question.

u have 1 file but have 2 different strings for the paths:

as in

Path 1 is C:\Docs\abc.txt

Path 2 is D:\Prog\Desktop\abc.txt

put the two paths in 2 string arrays. parse the arrays backwards till u reach the '\', from that point on again go forward till the end of the array and store this in 2 new arrays.

now compare these 2 arrays to chk if they are the same.

  • 0
  df_dukkar said:
so let me see if i'm getting the question.

u have 1 file but have 2 different strings for the paths:

as  in

Path 1 is C:\Docs\abc.txt

Path 2 is D:\Prog\Desktop\abc.txt

put the two paths in 2 string arrays. parse the arrays backwards till u reach the '\', from that point on again go forward till the end of the array and store this in 2 new arrays.

now compare these 2 arrays to chk if they are the same.

586278450[/snapback]

He wants to see if the files are the same, i.e. they contain the same stuff, but for some reason he doesn't want to open the file or uses hashes like an MD5sum.

  • 0

Sorry, let me reexplain :pinch:

c:\documents and settings\file.txt

c:\docume~1\file.txt

Technically, both are the same file, but doing a string comparison would say differently.

I have a function which has two parameters, inputfile and outputfile. If the outputfile is different than the inputfile, it will truncate the outputfile. But if the inputfile and outputfile are the same file, then it'll overwrite the current file.

I already mentioned that I could convert both strings to a short filename, but I'm unsure if there are other things to consider. For example, %systemroot%.

So I need a "foolproof" way of testing if the two strings both literally represent the same file. If converting to a short filename would be adequate, could someone give me a function that can do this? I was unable to find anything on Google or MSDN :blush:

And sorry for not being clearer in my first post :(

Btw, love your avatar - reminds me of when I was creating demos in DOS and I made effect that looked exactly as your avatar... heh..

My avatar is a XOR effect, (X ^ Y) ;)

Edit: Just to be absolutely sure I don't confuse anyone again...

I'm NOT looking to compare the contents of files.

I'm only looking to see if two file paths are the same.

eg. c:\docume~1\file.txt IS c:\documents and settings\file.txt. Only difference is one is the short file name and the other is the long file name.

Edited by xinok
  • 0

I dont really get why you would like to do that since they are always the same. That means instead of writing

cd "c:\documents and settings"

you can always use

cd c:\docume~1\

But if you really want to do that then it's only matter of stripping strings.

Reason that it stands docume~1 is that DOS cannot handle filenames larger than 8 characters, so "documents and settings" became "docume~1".

My recomendation is that you have some kind of translation table that translates docume~1 to its full name or use full path as input and strip it down to 6 characters and add "~1" to it.

  • 0
  xinok said:
but I'm not sure if Windows has other ways of linking files to eachother.

586278291[/snapback]

unfortunately windows does not have symlinks like in unix - this is how i understand link of similar (the same) files.

maybe i did not understand your post correctly, but if you want it not as part of some school assignment, what's the problem using 'comp' command?

i have it in the sendTo menu..

  • 0

NTFS supports both hard and soft links like ext2; these features are largely underused though.

There is an api function called GetShortPathName that will deal with 8.3 vs long format. The best way to detect all links/short/long would be to check which directory entry the directories ultimately point to. I think this approach would work only on a per-file-system basis (e.g., you need diff code for FAT32 and NTFS).

  • 0

Jayzee: I know what short file names are.

Andareed: Thanks for the GetShortPathName function

robotnic: I found this: CreateHardLink. It doesn't seem to exist in VC++ 6 though. I was hoping to create a hard link file, see what I can find out about them.

Taken from here:

A hard link to a file is indistinguishable from the original name for the file; there's no particular link that is more the "real name" for the file than any other.

I guess there isn't much I can do about hard link files.

Off Topic

Something thats just sort of bugging me, whats with all the typedef's and #define's in the C++ headers?

typedef LPCSTR LPCTSTR; typedef CONST CHAR *LPCSTR, *PCSTR; #define CONST const, typedef char CHAR; etc.

I really don't see the point. It just makes C++ harder to learn trying to memorize all these "types", and overall makes code harder to read if you don't know what a certain typedef or define is.

  • 0

I've actually written 2 apps for creating soft and hard links. If anyone wants, I can post them.

If you use CreateHardLink, you'll probably need to install the platform sdk and change the vc++ includes/libs directories. Interestingly, there is a new CreateSymbolicLink on msdn that only works with longhorn.

@xinok: these namings are generally acronyms. LPCTSTR means Long Pointer Const null-Terminating STRing. Another one is TCHAR, which is CHAR on ANSI and WCHAR on UNICODE. CHAR is char because win32 uses all caps for structures and primitives.

  • 0
  Andareed said:
I've actually written 2 apps for creating soft and hard links. If anyone wants, I can post them.

586280364[/snapback]

I'd appreciate it if I can get those apps :yes: And thanks ahead of time.
  • 0

Alright, I was able to solve this little riddle. First, creating a hard link file can be done from a command in windows:

fsutil hardlink create c:\output.txt c:\input.txt

Now testing for duplicates (I already tried this, it also locks hard link files):

We have the inputfile and outputfile

First, open the inputfile, but deny access to all other processes (lock the file)

Now try opening the outputfile. If it succeeds, the files are different. If it fails, continue...

Unlock the inputfile, and try opening the outputfile again. If it succeeds this time, then the files are the same. If it fails again, something else is wrong so return an error. :)

  • 0

Couldn't find softlink app but I based it on the code from here: http://www.codeproject.com/w2k/junctionpoints.asp

The hardlink app just uses CreateHardLink. There is also a sysinternals tool with source called junction: http://www.sysinternals.com/Utilities/Junction.html

  • 0
  df_dukkar said:
could u tell me how to lock down a file ??

586282181[/snapback]

I used the OpenFile function.

#include <windows.h>

char* file = "file.dat";

OFSTRUCT fileinfo;

long handle = OpenFile(file, &fileinfo, OF_SHARE_EXCLUSIVE);

  • 0
  Quote
PIDL's are only used in the shell.

That doesn't mean that you can still use them, if theu turn out to be usefull for your purpose.

You're right about hard and soft links tho. Maybe it's possible to use one of those Nt* API's to determine the file-block they 'link' too.

This topic is now closed to further replies.
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Posts

    • Consumer Reports is flat out wrong. Wouldn't be the first time it's a fact that when you have more moving parts, you have more room for failure. Less points of failure when all you replace on an EV is the tires and the wipers.
    • WYSIWYG Web Builder 20.2.2 by Razvan Serea Web Buialder is a WYSIWYG (What-You-See-Is-What-You-Get) program used to create complete web sites. WYSIWYG means that the finished page will display exactly the way it was designed. The program generates HTML (HyperText Markup Language) tags while you point and click on desired functions; you can create a web page without learning HTML. Just drag and drop objects to the page position them "anywhere" you want and when youre finished publish it to your web server (using the build in Publish tool). Web Builder gives you full control over the content and layout of your web pages. One Web Builder project file can hold multiple web pages. Desktop publishing for the web, build web sites as easy as Drag & Drop "One Click Publishing" No FTP program needed. No special hosting required, use with any Hosting Service! Easily create forms using the built-in Form Wizard plus Form validation tools and built-in CAPTCHA. Advanced graphics tools like shapes, textart, rotation, shadows and many other image effects. Fully integrated jQuery UI (Accordion, Tabs etc), animations, effects and built-in ThemeRoller theme editor. Google compatible sitemap generator / PayPal eCommerce Tools Many navigation tools available: Navigation bars, tab menus, dropdown menus, sitetree, slidemenus. Built-in Slide Shows, Photo Galleries, Rollover images, Banners etc. Support for YouTube, Flash Video, Windows Media Player and many other video formats. Unique extension (add-on) system with already more than 250 extensions available! Create HTML5 / CSS3 websites today HTML5 document type (optimized HTML5 output). HTML5 audio/video and YouTube HTML5 support. HTML5 forms: native form validation, new input types and options, web storage. HTML5 canvas and svg support in shapes and other drawing tools. CSS3 @font-face. Use non web safe fonts in all modern browsers. CSS3 opacity, border radius, box shadow. CSS3 gradients. Add cool gradient effects using native CSS3 (no images). CSS3 navigation menu. Create awesome menus without using JavaScript or images. CSS3 animations and transitions. Including support for 2D and 3D transforms! Features for advanced users: Login Tools/Page Password Protection. Built-in Content Management System with many plug-ins (guestbook, faq, downloads, photo album etc). Add custom HTML code with the HTML tools. JavaScript Events: Show/hide objects (with animation), timers, move objects, change styles etc. Layers: Sticky layer, Docking layer, Floating layer, Modal layer, Anchored layer, Strechable layer and more! jQuery Theme Manager, create your own themes for the built-in jQuery UI widgets. Style Manager (global styling, H1, H2, H3 etc). Master Frames and Master Objects: reuse common element in your website. and much more! WYSIWYG Web Builder 20.2.2 changelog: Improved: Minor change in HTML formatting of the Overlay Menu. Fixed: Issue with aspect ratio of HTML Video. Download: WYSIWYG Web Builder 64-bit | 30.1 MB (Shareware) Download: WYSIWYG Web Builder 32-bit | 28.0 MB Screenshot: >> Click here << Link: Home Page | Templates | Free extras/addons | Changelog Get alerted to all of our Software updates on Twitter at @NeowinSoftware
    • You are like that narcissistic moron and his name is Paul Thurrott.
  • Recent Achievements

    • Collaborator
      Mighty Pen went up a rank
      Collaborator
    • Week One Done
      emptyother earned a badge
      Week One Done
    • Week One Done
      DarkWun earned a badge
      Week One Done
    • Very Popular
      valkyr09 earned a badge
      Very Popular
    • Week One Done
      suprememobiles earned a badge
      Week One Done
  • Popular Contributors

    1. 1
      +primortal
      568
    2. 2
      +FloatingFatMan
      188
    3. 3
      ATLien_0
      177
    4. 4
      Skyfrog
      111
    5. 5
      Xenon
      110
  • Tell a friend

    Love Neowin? Tell a friend!