vector of doubles to QByteArray

[yan]

Hi.
Why you don't use QDataStream to unpack?

Your problème is maybe linked with the endian or float représentation use to write float to QByteArray

[gmseed]

Hi

QDataStream feeds through to the underlying QByteArray so I chose to operate on that directly.

Graham

[yan]

QDataSTream work in big endian by default.
http://doc.trolltech.com/4.6-snapsho...ByteOrder-enum


try qFromBigEndian to convert endian on the float readed.
http://doc.trolltech.com/4.6-snapsho...romBigEndian-2

[gmseed]

Hi

The only way I could et it to work is to work through QDataStream for both << and >>; see pasted code below.

I need to index into the packed byte array and found:

QIODevice* device = in.device();

works on the underlying internal QBuffer.

As illustrated in the first post, if I operate on the QBuffer outside of the QDataStream I can't get it to work.

It's a strange one and can only think that if QDataStream is used throughout then the encoding is consistent.

Cheers

Graham

void testAddVertices(const QVector<VertexType>& vertices)
{
	int numberVertices = vertices.size();
 
	QByteArray	byteArray;
	QDataStream out(&byteArray,QIODevice::WriteOnly);
 
	//double vx, vy, vz; // 64bit
	float  vx, vy, vz; // 32bit
	for (int i=0; i<numberVertices; i++)
	{
		const VertexType& v = vertices[i];
		vx = v.x(); vy = v.y(); vz = v.z();
		out << vx; out << vy; out << vz;
	}
 
	std::cout << "byteArray length: " << byteArray.length() << std::endl;
 
	// extract
	QDataStream in(&byteArray,QIODevice::ReadOnly);
	QIODevice* device = in.device();
	qint64 vertexComponentLength = 4;
	qint64 vertexLength = 3*vertexComponentLength;
	qint64 seekPos = 0;
	qint64 numberBytesRead;
	bool   toOK, seekOK;
	float currentValue;
	//float vx, vy, vz;
	for (int i=0; i<numberVertices; i++)
	{
		// seek to start of new vertex
		device->seek(seekPos);
		in >> vx;
 
		device->seek(seekPos+vertexComponentLength);
		in >> vy;
 
		device->seek(seekPos+2*vertexComponentLength);
		in >> vz;
 
		VertexType v(vx,vy,vz);
		std::cout << "v(" << vx << ", " << vy << ", " << vz << ")" << std::endl;
 
		// move to start of next vertex
		seekPos += vertexLength;
	}
}

void testAddVertices(const QVector<VertexType>& vertices)
{
	int numberVertices = vertices.size();

	QByteArray	byteArray;
	QDataStream out(&byteArray,QIODevice::WriteOnly);

	//double vx, vy, vz; // 64bit
	float  vx, vy, vz; // 32bit
	for (int i=0; i<numberVertices; i++)
	{
		const VertexType& v = vertices[i];
		vx = v.x(); vy = v.y(); vz = v.z();
		out << vx; out << vy; out << vz;
	}

	std::cout << "byteArray length: " << byteArray.length() << std::endl;

	// extract
	QDataStream in(&byteArray,QIODevice::ReadOnly);
	QIODevice* device = in.device();
	qint64 vertexComponentLength = 4;
	qint64 vertexLength = 3*vertexComponentLength;
	qint64 seekPos = 0;
	qint64 numberBytesRead;
	bool   toOK, seekOK;
	float currentValue;
	//float vx, vy, vz;
	for (int i=0; i<numberVertices; i++)
	{
		// seek to start of new vertex
		device->seek(seekPos);
		in >> vx;

		device->seek(seekPos+vertexComponentLength);
		in >> vy;

		device->seek(seekPos+2*vertexComponentLength);
		in >> vz;

		VertexType v(vx,vy,vz);
		std::cout << "v(" << vx << ", " << vy << ", " << vz << ")" << std::endl;

		// move to start of next vertex
		seekPos += vertexLength;
	}
}

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[yan]

For me this work perfectly

#include <QtCore>
 
int main(int argc, char *argv[])
{
 
    QByteArray byteArray;
 
    //generate ten random float value
    QVector<float> v;
    for (int i =0; i < 10;++i)
    {
        v << 100. * qrand()/RAND_MAX;
    }
    //ouput vector
    qDebug() << v;
 
    //write float value to array
    {
        QDataStream out (&byteArray,QIODevice::WriteOnly);
        foreach(float f,v)
        {
            out << f;
        }
    }
 
    //read all float from array
    QVector<float> v2;
    {
        QDataStream in(byteArray);
        while (!in.atEnd())
        {
            float f;
            in >> f;
            v2 << f;
        }
    }
    //ouput vector
    qDebug() << v2;
 
 
    return 0;
}

#include <QtCore>

int main(int argc, char *argv[])
{

    QByteArray byteArray;

    //generate ten random float value
    QVector<float> v;
    for (int i =0; i < 10;++i)
    {
        v << 100. * qrand()/RAND_MAX;
    }
    //ouput vector
    qDebug() << v;

    //write float value to array
    {
        QDataStream out (&byteArray,QIODevice::WriteOnly);
        foreach(float f,v)
        {
            out << f;
        }
    }

    //read all float from array
    QVector<float> v2;
    {
        QDataStream in(byteArray);
        while (!in.atEnd())
        {
            float f;
            in >> f;
            v2 << f;
        }
    }
    //ouput vector
    qDebug() << v2;


    return 0;
}

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