[Solved] Duplicate finder

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....

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.