[Solved] Duplicate finder

[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....

[ixSci]

Gerolf, thank you for the function name correction.
And yes, you are right about the question. I've misinterpreted OP goal :)

[alex.dadaev]

How do you think, is it correct?
@
while(it.hasNext())
{
it.next();
if(it.peekPrevious().key()==it.peekNext().key())
std::cout<<it.peekPrevious().value()<<"="
<<it.peekNext().value()<<std::endl;
}
@

[goetz]

No it is not correct.

It compares only adjacent entries in your container.

If your container is a map (QMap or QHash) and you use insert() to populate it then you will get no duplicates at all, since every key occurs only once, hence the keys at different positions are all distinct.

You must use insertMulti() and values() to get a list of all entries with the same hash value. Or use QMultiMap/QMultiHash with the before mentioned methods.

[alex.dadaev]

Yes, you're right, thanks

[alex.dadaev]

i can't understand why it's not working :(
@
while(it.hasNext())
{
it.next();
if(it.key()==it.peekNext().key()) {
std::cout << "i've got you" << std::endl;
}
}
@

PS: i've used insertMulti() to add item to hash, as you said

[alex.dadaev]

maybe like this?
@int compare_flag;

while(it.hasNext())
{
    it.next();
    compare_flag = QString::compare(it.key(),it.peekNext().key(),Qt::CaseSensitive);
                   if(compare_flag==0) {
        std::cout << "i've got you" << std::endl;
    }
}@

[goetz]

The keys in a (hash) map are always distinct. You will never find two identical keys so your comparison will never be true.

And even if you had identical keys in your container you would only find them if they are adjacent in the list.

But I'm going to have a kind of déjà-vu...

To make things clearer for us to understand: You do have a multi hash/multi map. What do you put in there and what do you expect to come out?

[alex.dadaev]

@QHash<QString,int> FilesHash;@
QString key is MD5
int value - just a number of file

on output i want to see the names of similar files

[goetz]

Ok, let's make things clearer step by step. Seems that you should make yourself comfortable with the concepts of a map.

A map (QHash is one) stores values associated with keys. Every key only exists once in the map - I wrote that several times, let's prove it:

@
QHash<QString, int> myHash;
myHash.insert("abc", 2);
myHash.insert("def", 3);
myHash.insert("abc", 5);

qDebug() << "hash keys:" << myHash.keys();

QHash<QString, int> myMultiHash;
myMultiHash.insertMulti("abc", 2);
myMultiHash.insertMulti("def", 3);
myMultiHash.insertMulti("abc", 5);

qDebug() << "multi hash keys:" << myMultiHash.keys();
@

What will the output be?

What will happen if you compare every key with every other?

[alex.dadaev]

insertMulti allows you to store items with similar keys

[alex.dadaev]

without overwriting them

[alex.dadaev]

what do you think about it?
@
bool ok;
QHashIterator<QString,int> it(FilesHash);
QHashIterator<QString,int> begin(FilesHash);
QHashIterator<QString,int> end(FilesHash);
while(it.hasNext()) {
it.next();
begin = qLowerBound(FilesHash.begin(), FilesHash.end(), it.key());
end = qUpperBound(begin, FilesHash.end(), it.key());
iter = begin;
while(iter!=end) {
if(*i=*it) {
ok = true;
} else { ok = false; }
}
}
@

[alex.dadaev]

why i cannot do like this?
@QHashIterator<QString,int> iter(FilesHash);

while(it.hasNext()) {
    it.next();
    iter = qBinaryFind(FilesHash.begin(), FilesHash.end(), it.key());
}@

[alex.dadaev]

please note that the problem has been solved :)

[giesbert]

you can do it on your own:
go to your first post and click edit :-)
and edit the title.