[Solved] Duplicate finder

goetz

If two hashes are equal then it is very likely that the two files they are computed of bitwise equal content (although not guaranteed as the set of all possible file contents is indefinite, whereas the number of possible hashes is limited and thus there cannot exist an isomorphic relation between them). You can store the hashes in a database and search for duplicates in that. For "similar" files you'll have to go with Levenshtein or other means, as Denis stated.

alex.dadaev

But how can i store file info in a hash ?

DenisKormalev

You can pass it contents through hash function and you will have it hash at the end.

goetz

[quote author="alex.dadaev" date="1295897294"]But how can i store file info in a hash ?[/quote]

You cannot. This "web page":http://lmgtfy.com/?q=hash+function has some explanations for you.

alex.dadaev

Okay :)

alex.dadaev

Is there any way to use QHash methods in QCryptographicHash ?
I'd like to make a comparing table for files that i hash.

tobias.hunger

QHash is a hash table, a datastructure optimized for random access based on a key value.

QCryptographicHash is used to calculate cryptographic hash values from input data. They are completely different things:-)

So, no, you can not use QHash's methods in QCryptographicHash. Just use the result of a QCryptographicHash as a key to a QHash and you should be set. Just make sure to reset the QCryptographic hash whenever you are done with a file, or you will not get the same hash values for the same files (since the second one will still have all the data of the first one "prepended").

goetz

Yes, that's possible. You can use the following function as a start for your project:

@
#define MY_SHA1_BUFFER_SIZE 4096

QString getSha1HashFromFile( const QString &fn )
{
QCryptographicHash ch( QCryptographicHash::Sha1 );
QFile file( fn );
if( !file.open( QIODevice::ReadOnly ) )
return QString();

char buf[MY_SHA1_BUFFER_SIZE];
while( !file.atEnd() ) {
    qint64 read = file.read( buf, MY_SHA1_BUFFER_SIZE );
    ch.addData( buf, read );
}
file.close();
return QString( ch.result.toHex() );

}
@

alex.dadaev

how can i make QString from QFileInfoList ?
is there any possibilities to do that?

giesbert

QFileInfo::path() ???

goetz

No.

QFileInfoList is a typedef for QList<QFileInfo>.

You know how many properties a QFileInfo object describing a single file has, don't you?

If you want a single string from these big bunch of information you will have to construct it yourself.

giesbert

Ok, forgpot to add the iteration by for(...)...

alex.dadaev

but how can i construct a path of a single file?

goetz

Read the docs on "QFileInfo":http://doc.qt.nokia.com/stable/qfileinfo.html - we did it too. Everything you need is documented there. Yes, it takes some 5 minutes to read it all through, but if you're too lazy we can't help you. If you have concrete questions or problems with any of the methods, ask them.

giesbert

If you read the documentation, you would find it ...

@
QFileInfoList list;
for(int i = 0; i < list.size(); ++i)
{
QString filePath = list[i].absoluteFilePath();
{
@

alex.dadaev

i've made it by myself already :) the reason why i ask so dumb questions is because i'm just starting using Qt and programming itself and i just want not to make stupid mistakes.
@QString path[list.size()];for (int i = 0; i < list.size(); ++i) {
QFileInfo fileInfo = list.at(i);
path[i] = fileInfo.path();}@

giesbert

I would suggest using a QStringList instead of QString path[xx];

goetz

First: Then show us your code and we comment on it; Don't ask dumb questions that are clearly answered in the very good API docs the Trolls have created for us. It is very likely that you will not get any answer (apart from "RTFM"). We all put some valuable amount of time into DevNet to answer questions - with that silly game you are stealing this time!

Second: Do not use C-Style arrays in C++ if you are not absolutely forced to. Use the fine "Container Classes":http://doc.qt.nokia.com/stable/containers.html of Qt (or the equivalents of C++ standard library or boost). In your case "QStringList":http://doc.qt.nokia.com/stable/qstringlist.html is what you want.

Third: C-Style arrays of unknown size at compile time are not supported by all compilers and therefore not portable. I leave you to google or bing to search for the details.

ixSci

Don't you think a hash computation is a little bit overkilling in the file duplicate determination?
Just read your files' contents into memory blocks and compare them with memcmp. If you may have big files it would be wiser to compare them block-by-block rather then the whole files at once.

Upd. function name

giesbert

memcpy copies in memory and does not compare them.

AFAIK, he wanted to search for duplicates, so hashes would be faster. YOu don't want to do a full compare for all files with all files....