Weird characters in file path

stretchthebits

I saw this from one of the examples. The example is called tabdialog

The constructor of the window class has
QFileInfo fileInfo(filePath);

where filePath is "."

and
fileInfo.absoluteFilePath()
somehow has the file path to the executable. It returns a QString.
It seems to be coded as 32 bit characters. I think it is wchar_t array. I’m not sure since the page about it doesn’t say much.
https://doc.qt.io/qt-5/qfileinfo.html

How can I convert that to ASCII 8 bit which is what I use else where in my program.

I tried
QString stringThing=fileInfo.absoluteFilePath();
strcpy(pstring, (const schar *)pqString.toLocal8Bit());
strcpy(pstring, (const schar *)pqString.toUtf8());

It doesn't seem to work.
What's the difference between these 2 functions?

SGaist

Hi,

The first one like explained in the documentation will use QTextCodec::codecForLocale to convert the text.
The other will turn your text into UTF8.

In any case, they both return a QByteArray, so your cast is wrong

stretchthebits

I tried
char pstring[1000];
QString stringThing=fileInfo.absoluteFilePath();
QByteArray ztest;
QTextCodec *codec=QTextCodec::codecForName("UTF-8");
ztest=codec->fromUnicode(stringThing);
strcpy(pstring, ztest.constData());

Instead of getting
/home/jake.......and so on

I am getting
80
21
-2/254
-1/254
-1/254
127

in my char array.

Can I get a clear example on how to use these classes?

SGaist

Why did you stop using toUt8 ?
By the way, what OS are you on ?

stretchthebits

Both functions,
pqString.toLocal8Bit()
pqString.toUtf8()
return the same data.
I inspected the first 9 elements.
I am on Kubuntu 18.04.4 LTS.
I just need to understand what I am getting? I am willing to write my own function to convert the unicode to ASCII 8 bit.

Christian Ehrlicher

@stretchthebits said in Weird characters in file path:

to ASCII 8 bit.

You don't want ascii - you want probably utf-8 which is returned by toUtf8(). toLocal8Bit() returns the current locale encoding which is utf-8 on most linux systems too.

stretchthebits

if toUtf8() does return a UTF-8 encoding, why does a path such as /home/joe/Documents looks like corrupted data when I copy to a char array?

fcarney

@stretchthebits said in Weird characters in file path:

strcpy(pstring, (const schar *)pqString.toUtf8());

Because this is bad code. toUtf8() returns a QByteArray (as @SGaist said), not a char* compatible string. You should avoid old styles casts unless absolutely necessary.
You should be doing:

QString stringThing=fileInfo.absoluteFilePath();
QByteArray tempbytes(pqString.toUtf8());
strcpy(pstring, tempbytes.data());

https://doc.qt.io/qt-5/qbytearray.html

stretchthebits

@fcarney said in Weird characters in file path:

QString stringThing=fileInfo.absoluteFilePath();
QByteArray tempbytes(pqString.toUtf8());
strcpy(pstring, tempbytes.data());

That worked but I would like to understand what is happening under the hood. I thought QByteArray was an array of char. That is what my test had shown. What changes is the QByteArray class making to the array returned by toUtf8()?

fcarney

Look at the source to the header for QByteArray. It has much more than char data in that class. By casting the entire object to a char array pointer you were pointing to other data besides the actual char data. That is why you needed to create a local QByteArray (not a temporary) and then access the char data via the .data() method of the QByteArray.

stretchthebits

Wow, if I use F11 to jump into the code, I get the sequence
Q_REQUIRED_RESULT QByteArray toUtf8() const &
{ return toUtf8_helper(*this); }

QByteArray QString::toUtf8_helper(const QString &str)
{
return qt_convert_to_utf8(str);
}

inline int size() const { return d->size; }

template <typename String, if_compatible_qstring_like<String> = true>
QStringView(const String &str) noexcept
: QStringView(str.isNull() ? nullptr : str.data(), qsizetype(str.size())) {}

static QByteArray qt_convert_to_utf8(QStringView str)
{
if (str.isNull())
return QByteArray();

return QUtf8::convertFromUnicode(str.data(), str.length());

}

and so on.
I guess I am a little behind the times. I'm not sure what all the
reinterpret_cast and
const_cast was about.
This is some fancy coding :)

I thought pqString.toUtf8() is suppose to return UTF-8 which should contain my path to the file
/home/john/bla bla and I could just pass that to fopen(). isn't UTF-8, the first 0 to 127 values encoded just like ASCII?
In other words, a array that contains /home/john/bla bla
whether encoded in UTF-8 or ASCII, they would be exactly identical.