QDataStream writing wrong values

[alok9871]

Hi

I wish to write something onto a data file. I thought of using QDataStream, but it tens to give me wrong output.

QFile file("file.dat");
 file.open(QIODevice::WriteOnly);
 QDataStream out(&file);
 out.setByteOrder(QDataStream::LittleEndian);
 //out << QString("the answer is");   // serialize a string
 int x = 54;
 out << (qint32)x;
 out.device()->close();

QFile file("file.dat");
 file.open(QIODevice::WriteOnly);
 QDataStream out(&file);
 out.setByteOrder(QDataStream::LittleEndian);
 //out << QString("the answer is");   // serialize a string
 int x = 54;
 out << (qint32)x;
 out.device()->close();

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I was expecting an output of 54. Itself it shouwing me its char value = 6; even with other numbers.

Please let me know how to address this problem

Thanks

Regards
Alok

[lanz]

If you need text output you should use http://qt-project.org/doc/qt-4.8/qtextstream.html instead.

QDataStream outputs data as sequence of bytes, not printable characters.

[ChrisW67]

Please let me know how to address this problem

There is no problem. QDataStream is outputting exactly what you asked it to. You have a 32-bit unsigned integer with the value 54 and you have asked for output in LittleEndian order. The integer is 4 bytes 0x00000036, and QDataStream outputs them in reverse order. You get 4 bytes in the file, the first is 54 decimal (0x36) followed by 3 zero bytes. Treated as text this is equivalent to the C string "6".

const int num = 54;
 
QFile out("out.txt");
if (out.open(QIODevice::WriteOnly) {
  QTextStream s(&out);
  s << num;
}

const int num = 54;

QFile out("out.txt");
if (out.open(QIODevice::WriteOnly) {
  QTextStream s(&out);
  s << num;
}

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Also look at QString::number(), QByteArray::number() etc.

[alok9871]

Thank you both for your amazing answers. Thanks Chris for the explanation. Learned something very useful.