[Qt-interest] Write struct in a QByteArray or QFile

[Oliver.Knoll at comit.ch]

Tiago Correia wrote on Monday, June 08, 2009 2:44 PM:

> Hi,
> 
> I'm trying to write my own struct to a file. I'm trying to use QFile,
> but I'm getting the correct data. 
> ...
> f.write( (char*) &wh, sizeof( WAVEHEADER ) );
> 
> Any ideias?

It is not very obvious from the docs http://doc.qtsoftware.com/4.5/qiodevice.html#write, but I think write() writes an 8-bit *string* (characters) to the file, that is it terminates when it encounters a NUL (\0) character (or when it has written 'maxSize' characters, whatever comes first). Actually the Qt docs only mention the *string* here: http://doc.qtsoftware.com/4.5/qiodevice.html#write-2, a method which was only introduced in Qt 4.5:

    "Writes data from a zero-terminated string of 8-bit characters to the device."

But I think this comment also applies to http://doc.qtsoftware.com/4.5/qiodevice.html#write.

Especially since there are methods in the API which specifically deal with *binary* data, such as:

  http://doc.qtsoftware.com/4.5/qiodevice.html#writeData

or maybe the version which takes a QByteArray as argument:

  http://doc.qtsoftware.com/4.5/qiodevice.html#write-3 (but not sure whether that also stops writing when it encounters NUL!).

You could also try something like this:

  QFile file("/some/path/data.bin");
  if (file.open(QIODevice::WriteOnly) == true) {
    QDataStream dataStream(&file);
    int nofBytesWritten = dataStream.writeRawData(static_cast<const char *>(&wh), sizeof(WAVEHEADER));
    ...
  } ...

Alternatively with the http://doc.qtsoftware.com/4.5/qdatastream.html#writeBytes flavour...

Cheers, Oliver
-- 
Oliver Knoll
Dipl. Informatik-Ing. ETH
COMIT AG - ++41 79 520 95 22