[SOLVED] Get extension of a file in Qt

[ashishbansal]

Hi Everyone,
I was searching for efficient method for finding the file extension in Qt but I was unable to found any. Although I can break it on "." and can use the right most part as the extension but that creates problem in multiple dots file name like for file named as "foo.tar.gz", it would only give gz.

So, Any hack-ish better solution?

Regards
Ashish Bansal

[maximus]

Have you checked QFileInfo

I think this can do it easily.
Good luck!

[ashishbansal]

@maximus said:

Have you checked QFileInfo

I think this can do it easily.
Good luck!

But that too splits the filename(both suffix and completeSuffix). If filename is foo.bar.tar.gz, I guess it is not gonna work.

[maximus]

@ashishbansal

Another way would be to find the first position on the dot "."
and take the right part as the extension

[ashishbansal]

@maximus said:

@ashishbansal

Another way would be to find the first position on the dot "."
and take the right part as the extension

But that too is not gonna work. Like in foo.bar.tar.gz, extension is tar.gz but it would give me bar.tar.gz

[maximus]

Usually what comes after the fist dot is the extension
Do you really have filename named that way? I don't..

[ashishbansal]

@maximus said:

Usually what comes after the fist dot is the extension
Do you really have filename named that way? I don't..

Yeah I have freedom-1.6.apk
or many other android applications having this type of name.

[maximus]

Can you show an actual file name (real) and what result you would like to get for the extension?
Thanks

[ashishbansal]

@maximus said:

Can you show an actual file name (real) and what result you would like to get for the extension?
Thanks

File name : freedom-1.6.apk
Result: freedom-1.6

Filename : data.tar.gz
Result: data

Filename: script.sh
Result: script

Filename: qt-everywhere-opensource-src-5.3.0.tar.xz
Result: qt-everywhere-opensource-src-5.3.0

I would like to get these result from the respective file names.

Thanks
Ashish Bansal

[Rondog]

If you had a list of known file extensions that you could compare to you could eliminate the guesses. It would be really good if you could get this list from the OS registered system file types. The list should be sorted (longest first, shortest last).

For example, your list might contain this:

{
.tar.gz
.tar.xz
.apk
.txt
.bat
.sh
}

and your program might do this:

for counter = 0 to size_of_list
  if file_name.ends_with(extension_list[counter]) then
    // found one
  end if
end for
// if extension not found then resort to 'hackery'.

That might be slow process if there are a lot of file extensions to check.

Note: A file may not have an extension so looking for one might cause problems. Also, some files have a file name that begins with a dot (hidden files in GNU/Linux or Unix) and may or may not have an additional extension at the end.

[maximus]

@Rondog

Seem like QFileInfo could do the work.

Have you tried
QString QFileInfo::baseName () const
It should returns file name with longest extension removed (file.tar.gz -> file)

[ashishbansal]

@Rondog @maximus

Well I solved it by making use of QMimeDatabase. Thanks!

QMimeDatabase db;
QString name("file3.3.tar.gz");
int length = name.length();
QList <QPair <int, QMimeType> > list;
for (int i = length; i > -1; i--) {
    QList<QMimeType> mimes = db.mimeTypesForFileName(name.section("", i, length));
    QMimeType mime = mimes.isEmpty() ? QMimeType() : mimes.last();
    if (mime.isValid() && (list.isEmpty() || list.last().second != mime)) {
        list.insert(list.count(), qMakePair(i, mime));
    }
}
if (!list.isEmpty()) {
    qDebug() << list.last();
}

As now I have i stored in list, I can take substring as answer.

[CodingCobra]

Simply use QFileInfo.completeSuffix. This will return the extension.
Hope this helps

[KroMignon]

@ashishbansal said in [SOLVED] Get extension of a file in Qt:

I guess it is not gonna work

Why of course QFileInfo::completeSuffix() is working! Do you have made a try before telling it don't?

QFileInfo fi("/tmp/archive.tar.gz");
QString ext = fi.completeSuffix();  // ext = "tar.gz"

[wrosecrans]

@ashishbansal said in [SOLVED] Get extension of a file in Qt:

But that too is not gonna work. Like in foo.bar.tar.gz, extension is tar.gz but it would give me bar.tar.gz

Basically any library would have "bar.tar.gz" as the full extension for "foo.bar.tar.gz" -- there's nothing about the filename itself that makes bar and tar obviously distinct. So the only way to have tar.gz get picked out as special is try to try have a giant database of every possible file extension in the universe. And even if you had that, it would give unintuitive/inconsistent results tomorrow when somebody came out with a new one and it started seeing some but not others.

In practice, pretty much every general purpose library is just going to be splitting the name using generic rules.