[SOLVED] Deserializing QFile into QVector<double> fails

[Mr.Floppy]

Hi!

I know how to serialize and deserialize a QVector by following these descriptions http://qt-project.org/doc/qt-4.8/qdatastream.html#details
And it works. Qt can put doubles into a file and read them back just fine.

Now I have a binary file that contains a series of doubles which was created by a Delphi program.
Its size is about 126KB.

Reading it into a QByteArray works like this:
@
/* Reading the File into a ByteArray works */
QFile file(fileName);
if (!file.open(QIODevice::ReadOnly)) return 0;
QByteArray foo = file.readAll();
file.close();

qDebug() << foo.size(); // Output: 128020

@

When I try to read it into a QVector it fails. No matter what type I choose:
@
/* Reading into a QVector<anything> fails */
QFile file(fileName);
if (!file.open(QIODevice::ReadOnly)) return 0;
QDataStream in(&file);
QVector<quint8> bar;
in >> bar;
file.close();

qDebug() << bar.size();

/* Error Message:

• ASSERT failure in qAllocMore: "Requested size is too large!", file tools\qbytearray.cpp, line 73
• Invalid parameter passed to C runtime function.
• Invalid parameter passed to C runtime function.
• Error - RtlWerpReportException failed with status code :-1073741823. Will try to launch the process directly
  */
  @

Ultimately I want to read this File into a QVector<double>.
For this I have 2 options:

1. Get the latter code working.
2. Go through the QByteArray byte by byte and combine each 8 of them to a double.
3. Do it completely differently.

My questions are:

• Why does the reading into a QVector fail, when it works fine with a files I have created myself?

• How would you snip the QByteArray into doubles? Is there an easy way?

Kind regards!

schmaunz

[Mr.Floppy]

I helped myself with this:
@
// Open and read binary file contents
QFile file(fileName);
if (!file.open(QIODevice::ReadOnly)) return 0;
QByteArray foo = file.readAll();
file.close();
// Discard the 5 byte wide file header
qint32 i = 4;
// The first Value will be x
bool isX = true;
// Result containers
QVector<double> x;
QVector<double> y;
// Temporary byte array
QByteArray array;
while(i < foo.size())
{
// forget previous 8 bit
array.clear();
// read next 8 bit
for (quint8 j = 0; j < 8; j++)
{
array.append(foo.at(i+j));
}
// increment i
i += 8;
// get array pointer
char* b = array.data();
// reinterpret it to double
double* d = reinterpret_cast<double*>(b);
// sort values by x and y
if (isX)
{
x.append(*d);
isX = false;
}
else
{
y.append(*d);
isX = true;
}
}
qDebug() << x << y;
@

It works, but it is really really ugly.
I would be glad, if someone could guide me to a more elegant solution :)

Thanks in advance!

[andrep]

If your double data starts at offset 5 in QByteArray foo you could replace lines 13 through 41 by something like (untested!)
@double xy = reinterpret_cast<double>(foo.data() + 5);
int i = 0, n = (foo.size() - 5) / 2 / sizeof(double);
while (i < n) {
x.append(xy[i++]);
y.append(xy[i++]);
}
@

[Mr.Floppy]

Tested it is, it works out of the box and I like it :)
Thank you very much andrep!