data bytes in QChar than from QChar to QByteArray

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Hi,
I am trying to get data(8 Bytes) in QChar than save it into QByteArray because later i want to use each byte separately in my function.

QChar tempVar=*(QChar*) DeviceMsg.DATA;

expected Bytes from DeviceMsg.DATA would be something like 00ff22ff55001188

what i am looking for is

QByteArray qba;
qba.data()[0]     00
qba.data()[1]     ff
qba.data()[2]     22
qba.data()[3]     ff
..

question here is

how to convert from QChar to QByteArray?

Thanks for reading Question any help would be appreciated

Posted 10-Dec-15 21:59pm

XamBEE

Updated 10-Dec-15 22:02pm

v2

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Richard MacCutchan 11-Dec-15 4:21am

Can you not create the QByteArray direct from the DATA field?

XamBEE 11-Dec-15 10:04am

DATA is not string its 8 Byte

typedef struct
{
DWORD ID;
canMSGTYPE MSGTYPE;
BYTE LEN;
BYTE DATA[8];
} CANMsg;

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Jochen Arndt · Answer 1 · 2015-12-10T22:34:00

Solution 1

This would not work as expected because your input is a string (your example "00ff22ff55001188") containing 16 characters (QChar). If you need the bytes represented by two characters, you must get a character pair and convert it to a byte or just convert the whole string to a 64-bit value and split that into bytes.

A possible solution would be (assuming DeviceMsg is a QString with 16 characaters representing a 64-bit hex value):

C++

QByteArray qba;
qba.resize(8);
qulonglong val = DeviceMsg.toULongLong(NULL, 16);
for (int i = 0; i < 8; i++)
{
    // Get the low byte and store it in the byte array
    qba[i] = static_cast<char>(val & 0xFF);
    // Shift in next byte
    val >>= 8;
}

[EDIT]
According to the new information about DeviceMsg (see below comment) there is no need to use QChar and the solution is quite simple (see http://doc.qt.io/qt-5/qbytearray.html#QByteArray-1[^]):

C++

QByteArray qba((const char *)DeviceMsg.DATA, sizeof(DeviceMsg.DATA));

Posted 10-Dec-15 22:34pm

Jochen Arndt

Updated 11-Dec-15 4:30am

v4

Comments

XamBEE 11-Dec-15 10:01am

Input is not string its 8 Byte data

typedef struct
{
DWORD ID;
canMSGTYPE MSGTYPE;
BYTE LEN;
BYTE DATA[8];
} CANMsg;
DeviceMsg.DATA is 8 Byte not QString

Jochen Arndt 11-Dec-15 10:16am

See my updated solution.

XamBEE 11-Dec-15 10:28am

What does this error message mean?
Call of overloaded function 'QByteArray(BYTE[8], unsigned int)' is ambguous

Jochen Arndt 11-Dec-15 10:33am

Try casting as in my updated example.
[EDIT]
How is BYTE defined?
I assumed char, unsigned char, int8_t, uint8_t or something similar.

XamBEE 11-Dec-15 10:37am

Thanks,
would be nice if you can elaborate it for clarification.

Jochen Arndt 11-Dec-15 10:47am

When your DATA are of type (unsigned) char, they are already the type used by QByteArray so that there is no need for conversions.

The example uses the QByteArray constructor that excepts a pointer and the number of bytes (see Qt link).

I don't know exactly why you got the ambigous error here. From the Qt documentation it should not occur because the other constructors have different parameters. However, casting the parameter with (const char*) tells the compiler which of the possible constructors should be used.

Just an addition:
The above used casting is the 'dirty' (C style) way. With C++ it is better to use
static_cast<const char*>(DeviceMsg.DATA)
instead. That would produce an error if the data can't be casted (e.g. has a type that can't be casted to a character).

XamBEE 11-Dec-15 10:43am

QByteArray qba((const char *)msg.DATA, sizeof(msg.DATA));
qDebug()<<qba.data();
output is in Unicode characters something like....

C
D
E
F
G

Jochen Arndt 11-Dec-15 10:57am

The data are binary and not text. You would only see useful output when the binary data are a text representation. If for example a byte has the value 0x30, it is printed as '0'.
To get the hex digits as printable string use
qDebug << qba.toHex();

XamBEE 14-Dec-15 9:53am

To access the byte at a particular index position of 8 byte data [00 ff 22 ff 55 00 11 88]
qDebug()<<qba.toHex()[0];
return 8 not 88
how i can get full byte data?

Jochen Arndt 14-Dec-15 10:12am

It seems you have still problems with the difference between a byte (an 8-bit value) and a character (a one or multiple byte value representing a printable character; the number of used bytes depends on the used encoding like ASCII, ISO8850-x, UTF-8, UTF-16).

qba[n] will return the byte at position n (e.g. 0x88 for position zero).

qba.toHex() returns a human readable ASCII string of the hex value converting each nibble (that is a 4-bit value) into it's corresponding ASCII character code ('0' - '9', 'A' - 'Z').

When using qba.toHex()[n] you will get the ASCII character code at position n in the string (e.g. character '8' which has the code 0x38).