Solution:
"The documentation states that QFileDevice::size() returns the size of the file. If the function were to require an open file, its documentation would say that. By convention, Qt doesn't document non-requirements."

Use QFile::read(char* qint64).

QFile file(file_name); file.open(QFile::ReadOnly); QVector<float> x,y; while(!file.atEnd()) { QList<QByteArray> list = file.readLine().split(' '); if(list.count()==2) { x<<list[0].toFloat(); y<<list[1].toFloat(); } } qDebug()<<x<<y;

@Aramir said in QRegExp returning incorrect position due to codec ?:

ve seen many SD cards/emmc die in ereaders (devices I'm aiming for) therefore I'm trying to lower the write operations on it in order to not reduce their lifetime. That's it I think it's worth the trouble to figure out a solution to this problem instead of creating more and more e-waste.

Again a useless optimization due to a feeling. Optimize only when you can prove it's a problem and needs to be optimzied.

You SD-Card has likely a sector size of 512 or 1024 bytes. On top of this your filesystem may use a block size up to 64kb (NTFS, ext4 use 4kb ). So when you even change single byte in your file which is less than the sector size or block size it will write the whole sector/block.
It's just plain stupid and an over-complicating of things for nothing.

@SimonSchroeder
QDir is only for directories, not for files. So it is not a (suitable) candidate for general "file paths".

Hi,

If you really want to avoid using a database as already suggested in your other thread and here. Use a proper structure in your file like XML so that you can search through more easily.

@sierdzio, false alarm!

After reopening my project everything got built and no file existance errors were present. Your hint about adding QCoreApplication really helped!

@JonB Thanks for your insight. I did as you suggested and found one of my local variable's address a nullptr(though not sure where it came from). I changed a few lines of code and apparently, my code works fine now. @Christian-Ehrlicher @J-Hilk thanks!

@suslucoder said in Windows not responding on reading file from txt:

It works

so please don't forget to mark your post as solved!

What do you put in your QList ?

Can you explain what is the exact issue you are having with writing the content you are reading from the Excel file to another text file ?

Hi.

I think it just for a static QObject like QFile in Application ...
It can solve with static function to create a static object in first call...

@mrjj Thanks so much , really helped me understand.

@TUStudi
Ehh. :)
well you would on purpose made it so.
With the compiler and Qt version you choose to compile app with.
THe Qt used would be called UWP


So I would guess on its Not a "Metro" app.

But this can also just be something about windows version/patching and not related to you app as all.

https://docs.microsoft.com/en-us/answers/questions/3166/what-is-the-meaning-of-this-output-element-not-fou.html

@mrjj said in Writing to the file continuously in Qt (realtime data)?:

@SpaceToon
hi
Yes you just want to open it once.
But i dont see you calling flush anywhere ?

Oh, I forgot to paste the flush here, it is actually in my code directly after the write-statement. Thank you very much :)

@vishbynature
I don't claim to understand what the best way to do whatever you want here is. Maybe @Pablo-J-Rogina's suggestion of a database. The one thing I can tell you is that achieving whatever you are attempting by seeking to byte #80 in a text file and overwriting what is there is not the right approach.

If you want some solution which involves sticking with text files, it should look something like: open the existing file for read, open a new file for write, read stuff from old and write to new, making whatever modifications you wish as you go along, close both, delete old file, rename new to old. A few more steps than you wanted! Or, if file not too large, read whole file into some memory structure, make your changes there, write whole memory structure back to the file, completely replacing it.

@legitnameyo
Although what @Kent-Dorfman says about stack-allocated destructor auto-closing is quite correct, I would always put in an explicit close() as soon as I am finished with any file, personally. It's good practice, especially for potential future code changes. You never need flush() on read, and you don't need flush() on write if it's immediately followed by close().

@LeLev Thanks, I'll check it out!

@Dariusz Simply seek to the position where you want to read and then read the amount of bytes you need.
https://doc.qt.io/qt-5/qfiledevice.html#seek
https://doc.qt.io/qt-5/qiodevice.html#read-1

You can seek to the beginning of the file if you decide to read whole file.

@J.Hilk Thank You it did work. You saved me.