“plain/text” encodedData and QDataStream to readable QString

Question

I'd like to convert the following snippet to use "plain/text" mimetype without relying on QTextStream

 bool DragDropListModel::dropMimeData(const QMimeData *data,
           Qt::DropAction action, int row, int column, const QModelIndex &parent)
 {
  ...
  QByteArray encodedData = data->data("application/vnd.text.list");
  QDataStream stream(&encodedData, QIODevice::ReadOnly);
  QStringList newItems;

  while (!stream.atEnd()) {
   QString text;
   stream >> text;
   newItems << text;
  }
  ...
 }

I tried to apply what said at Qt parse string of undefined size from a binary data stream

 char *ch;
 QFile file("file.dat")
 file.open(QIODevice::ReadOnly);
 QDataStream in(&file)
 in >> ch;
 QString str(ch);

and http://www.qtcentre.org/threads/696-QDataStream-reading-into-QString

 stream.setByteOrder( QDataStream::BigEndian);
 ...
 quint16 id;
 stream >> id;  // First two bytes
 char* filename;
 stream >> filename; // String of undefined size
 QString file = QString::fromLatin1(filename);
 qDebug() << "output: " << file;
 newItems << file;
 delete[] filename; //cleanup

but I am always getting an empty string or 0. I am reading that "The only disadvantage to using QDataStream (over QTextStream) is that the resulting file is binary (i.e., not human readable)." Is there no way to convert QDataStream of plain text to readable QString?

Similar to QT QString from QDataStream but I'd like to read binary data from a stream through a loop and the << operator (indirect method).

Documentation at http://qt-project.org/doc/qt-5/qdatastream.html#details

ADD-ON

// drag&drop plain/text from outside the app is "abcdefg"

while (!stream.atEnd()) {
    char* a;
    stream.readRawData(a, 7); // abcdefg length = 7
    QString string(a);
    qDebug() << "output " << string; // WORKING => abcdefg
}

say I write the following code before the while loop:

quint8 v;
stream >> v;
qDebug() << "output: " << v; // => 97 = "a"

which is equivalent to

quint8 v;
stream >> v;
QString a;
qDebug() << "output: " << static_cast<char>(v); // => "a"

and the while loops crashes:
error: Exception at 0x5dd02907, code: 0xc0000005: read access violation at: 0x0, flags=0x0 (first chance)

my plain/text string doesn't seem to have length bytes at the beginning. I could run it as it is but I am wondering if I could determine the length of the string in advance. Whenever I try to read from the stream through the << operator, I can't simply reset it to the beginning.

elvisTeixeira elvisTeixeira · Accepted Answer · 2014-07-03T14:20:20

Try to modify the code

char *ch;
QFile file("file.dat")
file.open(QIODevice::ReadOnly);
QDataStream in(&file)
in >> ch;
QString str(ch);

to use char buf[BUF_SIZE] instead of char *ch, with BUF_SIZE a reasonable size for the file.

“plain/text” encodedData and QDataStream to readable QString

1 Answers