Reading Raw Data from File

jipe3001

Hi guys, I am trying to read a raw data file as follows:

 QFile fileName("C:/0data/QT Projects new/falcon/18071209.422");
fileName.open(QIODevice::ReadOnly);
 QDataStream in(&fileName);

QByteArray line_data(7,0);

while (!in.atEnd()) {

 in.readRawData(line_data.data(),7);

           v_lap     = line_data.mid(0,1);
           v_data1   = line_data.mid(1,1);
           v_data2   = line_data.mid(2,1);
           v_data3   = line_data.mid(3,1);
           v_data4   = line_data.mid(4,1);
           v_datacr  = line_data.mid(5,1);
           v_datalf  = line_data.mid(6,1);

           vlap_max = v_lap.toInt();
}

And here are the results:

Variables locales		
	line_data	"\001\030\030\000\030\r\n"	QByteArray
		v_data1	"\030"	QVariant (QByteArray)
		v_data2	"\030"	QVariant (QByteArray)
		v_data3	"\000"	QVariant (QByteArray)
		v_data4	"\030"	QVariant (QByteArray)
		v_datacr	"\r"	QString
		v_datalf	"\n"	QString
		v_lap	"\001"	QVariant (QByteArray)
		vlap_max	0	qint16

My concern is about the values who seems to be always seen as char despite a raw_data read and
when trying to convert v_lap to int the result is always 0 !!

Thks for your usual coop

JP

jipe3001

I finally succeed to read my file in Raw mode with QVariant as follows:

QFile fileName("C:/0data/QT Projects new/datafile");
fileName.open(QIODevice::ReadOnly);

QDataStream in(&fileName);

QByteArray record_data(1,0);

while (!in.atEnd()) {

    in.readRawData(record_data.data(),1);
    v_lap=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data1=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data2=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data3=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data4=(*record_data.constData());

}

and the result in the debugger is:

		v_data1	48	QVariant (int)
		v_data2	49	QVariant (int)
		v_data3	50	QVariant (int)
		v_data4	51	QVariant (int)

Thks to all of you for the support and sorry to not catch up so quick

JP

jsulm

@jipe3001 See http://doc.qt.io/qt-5/qbytearray.html#toInt
You should rather use QDataStream and do the conversion using its >> operators like http://doc.qt.io/qt-5/qdatastream.html#operator-gt-gt-4

J.Hilk

@jipe3001 said in Reading Raw Data from File:

thats because v_lap is a QVariant of type (QByteArray) theres most likly no conversion in QVariant that turns a QByteArray into a n int

try the following

v_lap     = line_data.mid(0,1).toInt();

thats still with some heavy copy and conversion operation but it should return the correct int.

VRonin

Why are you using QVariant?
QVariant::toInt on a QByteArray will use string conversion

My concern is about the values who seems to be always seen as char

char is the only type in the standard assured to have sizeof==1 so it is used to represent a "byte of data"

when trying to convert v_lap to int the result is always 0

What you want is int v_lapInt(*v_lap.toByteArray().constData());

jipe3001

Thks for all your answers but I guess my real problem is about the conversion to INT

For example I am reading the following QByteArray as follows:

QByteArray test_lap(1,0);
in.readRawData(test_lap.data(),0);

And I've got this in debuging mode monitor:

test_lap "\001" QByteArray
1 0x01 char

Therefore I tried to convert this Hexa value to Int as follows:

bool ok;
int x_lap2 = test_lap.toInt(&ok,16);

But the results are always:

ok false bool
x_lap2 0 int

What is wrong is this convertion which should be so simple?

jsulm

@jipe3001 You should really take a look at http://doc.qt.io/qt-5/qdatastream.html It greatly simplifies reading binary data.

mpergand

@jipe3001 said in Reading Raw Data from File:

test_lap "\001" QByteArray
1 0x01 char

It's not a ascii hex value,.

example:

const char* c="d";   // 13 hex
QByteArray arr= QByteArray(c);
int v=arr.toInt(0,16); // convert to binary
 qDebug()<<v; // display 13 in decimal (default)

\001 means 1 ( escape octal value)

const char* c="\011";   // 9 octal
QByteArray arr= QByteArray(c);
int v=arr.at(0); 
qDebug()<<v; // display 9 in decimal (default)

VRonin

@jipe3001 said in Reading Raw Data from File:

What is wrong is this convertion which should be so simple?

@VRonin said in Reading Raw Data from File:

toInt on a QByteArray will use string conversion
What you want is int v_lapInt(*v_lap.toByteArray().constData());

jipe3001

I finally succeed to read my file in Raw mode with QVariant as follows:

QFile fileName("C:/0data/QT Projects new/datafile");
fileName.open(QIODevice::ReadOnly);

QDataStream in(&fileName);

QByteArray record_data(1,0);

while (!in.atEnd()) {

    in.readRawData(record_data.data(),1);
    v_lap=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data1=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data2=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data3=(*record_data.constData());

    in.readRawData(record_data.data(),1);
    v_data4=(*record_data.constData());

}

and the result in the debugger is:

		v_data1	48	QVariant (int)
		v_data2	49	QVariant (int)
		v_data3	50	QVariant (int)
		v_data4	51	QVariant (int)

Thks to all of you for the support and sorry to not catch up so quick

JP