Reading binary file with maltlab format

[Lumbricus]

Hey guys,

i want to read a binary file which has been read with matlab with this format; 8x double in one line, varying number of lines depending on the file.

in matlab i can read it like this:

fid=fopen("filepath),'r')
initial_state = fread(fid, [8 inf],'double'); #


from the matlab documentation i found that a matlab double = 64Bits or 8Bytes

i am using a 64-bit version of qt. This is how i tried to read the file:

QFile binary("filepath.bin");
        binary.open(QIODevice::ReadOnly);
        QDataStream in(&binary);
        in.setFloatingPointPrecision(QDataStream::DoublePrecision);  //64-bit
        double d1,d2,d3,d4,d5,d6,d7,d8;
        in >>  d1 >> d2 >> d3 >> d4 >> d5 >> d6 >> d7 >>d8;
        qDebug() << d1 << d2 << d3 << d4 << d5 <<d6 << d7 <<d8;

QFile binary("filepath.bin");
        binary.open(QIODevice::ReadOnly);
        QDataStream in(&binary);
        in.setFloatingPointPrecision(QDataStream::DoublePrecision);  //64-bit
        double d1,d2,d3,d4,d5,d6,d7,d8;
        in >>  d1 >> d2 >> d3 >> d4 >> d5 >> d6 >> d7 >>d8;
        qDebug() << d1 << d2 << d3 << d4 << d5 <<d6 << d7 <<d8;

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From qt documentation:

QDataStream & QDataStream:perator>>(double & f)

i think this is what i need but i cant figure out how to use it. The output i am getting are not the output that matlab is reading. can someone point me in the right direction? cheers!

[anda_skoa]

Matlab is unlikely using QDataStream so you don't use it either.

Cheers,
_

[ChrisW67]

If the stored byte order is the same as you machine architecture.

Q_ASSERT(sizeof(double)==8);
QFile binary("filepath.bin");
if(  binary.open(QIODevice::ReadOnly) ) {
  double values[8];
  qint64 bytes = binary.read(static_cast<char *>(values), 64);
  if (bytes == 64) {
    for (int i = 0; i < 8; ++i)
      qDebug() << values[i];
  }
}

Q_ASSERT(sizeof(double)==8);
QFile binary("filepath.bin");
if(  binary.open(QIODevice::ReadOnly) ) {
  double values[8];
  qint64 bytes = binary.read(static_cast<char *>(values), 64);
  if (bytes == 64) {
    for (int i = 0; i < 8; ++i)
      qDebug() << values[i];
  }
}

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If the byte order is different then you have a byte swapping exercise to do.

With a primitive type (i.e. Known size) you might be able to use QDatastream but you still need to know the byte order and set the stream accordingly. That is not really QDataStream's purpose though.

[Lumbricus]

Thx guys, i took anda's tip and used standard c++ fopen and fread and reverse engineered the code that wrote the binary file to find out what format it has.

[anda_skoa]

You could have still used QFile and its read methods, just using QDataStream was too much

Cheers,
_