[SOLVED] String to double conversion failed and issues with qDebug

QG90

I'm receiving data from usb and i convert them to QString. Then the message is separated
to different variable. In the end i want these variables to double type but using the qDebug
my output is 0 "4, so 0 is for lat which means the conversion failed and "4 is for latitude
but why only the first character? The string is many bytes long.

@std::string message(usb_data.constData(), 60); //usb_data.length()
QString qmessage = QString::fromStdString(message);
QString latitude = qmessage.mid(0,21);
QString longitude = qmessage.mid(23,25);
QString height = qmessage.mid(50);

    QString lat_mid = qmessage.mid(0,18);
    QString lon_mid = qmessage.mid(23,21);




    double lat =  lat_mid.toDouble();
    double lon =  lon_mid.toDouble();

    qDebug() << lat << latitude;@

SGaist

Hi and welcome to devnet,

Can you show the content of latitude, longitude, lat_mid and lon_mid ?

QG90

hey nice to be here,
latitude contains something like 40.705465,E
longitude -74.026566,S
lat_mid 40.705465
lon_mid -74.026566

So i am removing the ,E and ,S to be able to convert to double but i get 0.
There might be non-printable characters messing with the conversion.

QG90

This line of code @qDebug() << lat_mid.toLatin1();@

outputs to this "4

this line of code @qDebug() << lat_mid.toLatin1().toHex();@

outputs to this "34003000340035002e003800390032003100"

I had a look at the "ascii chart":http://en.wikipedia.org/wiki/ASCII#ASCII_control_characters and apparently every
00 is misinterpreted to a null character.

andreyc

What is a result of std::cout instead of qDebug()
What is a result of using QByteArray as intermediate variable ?
@
QByteArray data = lat_mid.toLatin1();
qDebug() << data;
qDebug() << data.data();
@

QG90

[quote author="andreyc" date="1409010147"]What is a result of std::cout instead of qDebug()[/quote]

Don't know how to make this work. Even @std::cout << "asdf" << endl;@
doesn't show up anywhere. But it built.

[quote author="andreyc" date="1409010147"]What is a result of using QByteArray as intermediate variable ?
@
QByteArray data = lat_mid.toLatin1();
qDebug() << data;
qDebug() << data.data();
@
[/quote]

The result is "4 for the first and 4 for the second

andreyc

What about
@
QByteArray data = lat_mid.toLocal8Bit();
@

andreyc

Scratch my previous suggestions.
I think you need to write your own deserializer.

Something simple like skipping each other byte in a for loop.
Or using QByteArray and QDataStream
@
class MyData
{
...
QString toString() const;
};
QDataStream &operator>>(QDataStream &in, MyData &data);

QByteArray data = QByteArray::fromRawData(usb_data.constData(), 60);
QDataStream in(&data, QIODevice::ReadOnly);
MyData data;
in >> data;
qDebug() << data.toString();
@

andreyc

And one more attempt.

I guess that usb_data.constData() returns const char*
@
QString qmessage = QString::fromUtf16(reinterpret_cast<const unsigned short*>(usb_data.constData()));
@

[EDIT] Example
@
const char* latStr = "\x34\x00\x30\x00\x34\x00\x35\x00\x2e\x00\x38\x00\x39\x00\x32\x00\x31\x00";
QString str1 = QString::fromUtf16(reinterpret_cast<const unsigned short*>(latStr));
qDebug() << str1;
@
output
@
"4045.8921"
@

SGaist

By the way, what class is usb_data ?

QG90

[quote author="andreyc" date="1409012176"]What about
@
QByteArray data = lat_mid.toLocal8Bit();
@[/quote]

Still the same "4 and 4. I'll have a look at your other suggestion.

[quote author="SGaist" date="1409038961"]By the way, what class is usb_data ?[/quote]

It's Qbytearray.

QG90

[quote author="andreyc" date="1409020154"]And one more attempt.

I guess that usb_data.constData() returns const char*
@
QString qmessage = QString::fromUtf16(reinterpret_cast<const unsigned short*>(usb_data.constData()));
@

[EDIT] Example
@
const char* latStr = "\x34\x00\x30\x00\x34\x00\x35\x00\x2e\x00\x38\x00\x39\x00\x32\x00\x31\x00";
QString str1 = QString::fromUtf16(reinterpret_cast<const unsigned short*>(latStr));
qDebug() << str1;
@
output

"4045.8921"

[/quote]

I used your example @QString str1 = QString::fromUtf16(reinterpret_cast<const unsigned short*>(lat_mid));
qDebug() << str1;@

but i get an error @error C2440: 'reinterpret_cast' : cannot convert from 'QString' to 'const unsigned short *'@

QG90

Also this is how usb_data is created @QByteArray usb_data(reinterpret_cast<char*>(buf), sizeof(buf));@

andreyc

[quote author="QG90" date="1409047489"]
I used your example
@
QString str1 = QString::fromUtf16(reinterpret_cast<const unsigned short*>(lat_mid));
qDebug() << str1;
@
but i get an error
@
error C2440: 'reinterpret_cast' : cannot convert from 'QString' to 'const unsigned short *'
@
[/quote]

It want work. If I understand it correctly you are getting UTF16 string from USB. UTF16 contains zeros, not number 0 but ascii code 0. And it will break any standard string operations.
So, if you prefer to use standard string operations (QString etc) you need to translate you incoming buffer to a regular string.

[quote author="QG90" date="1409054635"]
Also this is how usb_data is created @QByteArray usb_data(reinterpret_cast<char*>(buf), sizeof(buf));@
[/quote]

Instead of converting buf to QByteArray convert it to QString
@
QString usbStr;
usbStr = QString::fromUtf16(reinterpret_cast<const unsigned short*>(buf), sizeof(buf));
@

And then
@
QString latitude = usbStr.mid(0,21);
QString longitude = usbStr.mid(23,25);
QString height = usbStr.mid(50);

QString lat_mid = usbStr.mid(0,18);
QString lon_mid = usbStr.mid(23,21);

double lat = lat_mid.toDouble();
double lon = lon_mid.toDouble();

qDebug() << lat << latitude;
@

QG90

It seems to work!!!! Now on qDebug i receive 4045.88 "4045.8783,N"
probably the 783 part on the number sums to an 8.

andreyc

Yep, looks like legitimate rounding.
I think qDebug() does rounding because I don't see any rounding rules in QString::toDouble().

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