Encode/decode to binary file

Cobra91151

So, here is the code example to create/write data to a binary file:

#include <QFile>
#include <QDataStream>
#include <QMessageBox>

void MainWindow::on_pushButton_3_clicked()
{
        QFile *myBinaryFile = new QFile(qApp->applicationDirPath() + "/myDataFile.dat");
        myBinaryFile->open(QIODevice::WriteOnly);
        QDataStream binaryDataStream(myBinaryFile);
        binaryDataStream.setVersion(QDataStream::Qt_5_9); //set QDataStream version for your Qt version if you need both forward and backward compatibility
        binaryDataStream << QString("This is a test...");
        myBinaryFile->close();
        myBinaryFile->deleteLater();
        QMessageBox::information(this, "Information", "Binary file created!", QMessageBox::Ok);
}

It writes a myDataFile.dat binary file to the application directory. If you want to read the data from the binary file, take a look at the documentation, the process will be similar. Happy coding!

Hollywood33

@Cobra91151 Thank you very much!

Hollywood33

@Cobra91151 Hi! I tried, file created but it's not binary, just plain test text in in.
I want it to look like this: 01101001010101010010.

J.Hilk

@Hollywood33 how do you think data is stored on your HD?

You happen to have a good text-editor that interpretes the 01's as ASCII-chars and displays them.

Not a problem of Qt but your external file-viewer.

I think what you want is to save Strings/Numbers as human readable 0/1 in a *.txt file. Correct?
Than you'll have to create a function that takes a String/Number and returns a fromated string, that you than can save into your file.

Hollywood33

@J.Hilk I opened it in TextEdit on mac, notepad in Win. You are right, I need sequence of "0" and "1" in .txt file. Please write example using QFileDialog.
It has to work with all file extensions and file sizes.

jsulm

@Hollywood33 said in Encode/decode to binary file:

It has to work with all file extensions and file sizes.

What does it have to do with file extension and file size?!
If I understood you correctly all you want to do is writing a text file containing 0 and 1 as characters, right?
File extension is simply part of file name and does not define its format. You could store a picture as "mypicture.xml" - it still would be a picture and not XML.
If you would have checked the documentation (http://doc.qt.io/qt-5/qfile.html) you would have found this:

QFile file("out.txt");
if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
    return;

QTextStream out(&file);
out << "The magic number is: " << 49 << "\n";

mrjj

Hi
I read it as he just want a binary file but do not understand that
some editors will not show the raw binary but show
it translated. So not sure he wants ASCII 0 and 1 but meant
it as a way to say binary which QDataStream already is :)

jsulm

@mrjj @Hollywood33 OK, then I would suggest to use a hex-editor instead of a text editor :-)

Hollywood33

@jsulm it writes plain text.
I want file to be saved in .txt file as sequence of 0 and 1. It must look like 01010001 in simple text editor, like Notepad, not HEX viewer.

jsulm

@Hollywood33 Then you want to write text. Because text editors (like the name suggests) only understand text. It wouldn't be a binary file. You would write 1 and 0 as characters:

QFile file("out.txt");
if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
    return;

QTextStream out(&file);
out << "010001100101110";

You need to understand the difference between text and binary. 0 as character in a text file is stored as ASCII number 48, 1 is 49. That means if you store 01 in a text file and open it in a hex editor you will see 4849 (or 0x30 0x31 as hex).

Hollywood33

@jsulm i know the difference between text and binary code.
I want to see 0&1's as UTF-8 text in *.txt file. What you have written is only writes text into file.

jsulm

@Hollywood33 '1' and '0' are same in ASCII and UTF-8 as far as I know...

J.Hilk

because I'm a good guy :-)

QString toBitString(const QVariant &v)
{
    QByteArray bytes = v.toByteArray();
    QString bitString;

    QChar Zero('0');
    QChar One('1');

    for(int y(0); y <bytes.size(); y++){
        for(int i(0); i < 8; i++){
            bool b = (bytes[y] >> i) & 1;
            bitString.append(b ? One:Zero);
        }
    }
    return bitString;
}

Edit:
Small edit in the code example, v.toByteArray().data() totally unnecessary!

Hollywood33

@J.Hilk It looks like what I need. It remains only to understand how to use it with QFileDialog.

mrjj

@Hollywood33
Hi
The docs shows how to use it.
http://doc.qt.io/qt-5/qfiledialog.html
It has sample :)

Cobra91151

@Hollywood33

Ok, here is the code how I would save it with QFileDialog class using @J-Hilk solution.

QString filters = "Text Documents (*.txt);;All files (*.*)";
QString filePath = QFileDialog::getSaveFileName(this, "Save binary file", qApp->applicationDirPath() + "/MyFile", filters, nullptr);

 if (!filePath.isEmpty()) {
      QFile *myFile = new QFile(filePath);
      myFile->open(QIODevice::WriteOnly);
      QTextStream myTextStream(myFile); //QTextStream is used because you want to save it in .txt file
      myTextStream << toBitString(QString("This is a test!"));
      myFile->close();
      myFile->deleteLater();
      QMessageBox::information(this, "Information", "Binary file is saved!", QMessageBox::Ok);
 }

mrjj

@Cobra91151
Hi
Just as a note.
There is really no need to new the QFile.
QFile myFile;
will work just as fine as it has no need to survive the scope/function.
but you do delete it so no leak but no real benefit :)

Cobra91151

@mrjj

Hi! Yes, you right, in this example better to use QFile myFile on the stack.

Hollywood33

@Cobra91151 can't build: nullptr is not declared in this scope;
tobitstring is not declared in this scope

mrjj

@Hollywood33
odd it dont know nullptr but you can use 0 (zero) or NULL instead
also just remove
myTextStream << toBitString(QString("This is a test!"));
--->
myTextStream << QString("This is a test!");