Converting QByteArray to unsigned char

[James Sprinks]

Hi all

I have a populated QByteArray - filled with hexadecimal numbers (0x01, 0x41 etc.).

I need to convert this to a unsigned char array of the same size. Any Ideas?

    QByteArray data;
    data[0] = 0x41;
    data[1] = 0x12;

    //Append ff codes to datastream (representing no change)
    for (int i = 0; i < 35; i++)
    {
        data.append(0xFF);
    }

    int count = data.size();
    unsigned char hex[count];

How do I populate the unsigned char hex with the contents of the QByteArray data?

Thanks

James

[VRonin]

unsigned char hex[count]; is invalid in C++, it only compiles if your compiler treats it as C, as far as I know only gcc does that by default

const std::size_t count = data.size();
unsigned char* hex =new unsigned char[count];
std::memcpy(hex,data.constData(),count);

[James Sprinks]

@VRonin I get this error with that code:

C:\PMPS\PMPSv1\pmps_f.cpp:1605: error: reinterpret_cast from type 'const char*' to type 'unsigned char*' casts away qualifiers
memcpy(hex,reinterpret_cast<unsigned char*>(data.constData()),count);
^

[VRonin]

@James-Sprinks I ninja'd in my correction. it was easy btw

[James Sprinks]

@VRonin So what is the correction?

[VRonin]

@VRonin said in Converting QByteArray to unsigned char:

std::memcpy(hex,data.constData(),count);

std::memcpy(hex,data.constData(),count); as written above

[James Sprinks]

@VRonin Brilliant. Thank you!

[VRonin]

On a side note, you could also use reinterpret_cast<unsigned char*>(data.data()) if you don't need to copy it to a separate array

[aha_1980]

Sorry for hijacking, but what do you guys think of QTBUG-64746?

It seems very common to use QByteArray as a raw byte container and sometimes you need unsigned char instead char.

[J.Hilk]

@aha_1980 I wouldn't be averse to it

I have a case were I check specific bytes for values first, before managing the whole byte array and some checks are higher than 0x7F.
The comparing operator ==(0xAA) works fine, but is always taged with a warning. Which tickles my OCD.

To your point made in the Bugreport-ticket.

In my current case, a QtSerialBus communication, I combine 2 chars to a short via QDatatStream.

{//section from my class
...
     QDataStream out(m_data);
     quint8 countData;
     QVector<quint16> values;
     out >> countData;
     countData = countData/2;

     quint16 value;
     for(int i(0); i <countData; i++){
           out >> value;
           if(out.status() == QDataStream::Ok)
                 values.append(value);
           }
      return values;    
}

I did this because I didn't want to use all the reinterpret_cast's. Tried it first, became unreadable pretty quickly x)

[aha_1980]

@J.Hilk said in Converting QByteArray to unsigned char:

I did this because I didn't want to use all the reinterpret_cast's. Tried it first, became unreadable pretty quickly x)

That's my motivation also. Of course QDataStream is the correct solution, but that's still a lot of code lines for a simple problem. And sometimes you just want to create a QByteArray with some values in it, which should be a one-liner IMHO.

[J.Hilk]

@aha_1980 said in Converting QByteArray to unsigned char:

And sometimes you just want to create a QByteArray with some values in it, which should be a one-liner IMHO.

verry true,
I'm missing a simple constructor/initalizer list functionality

for example:

//I wish this was possible 
QByteArray ba{0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80};

[guitarpicva]

Try the macro QByteArrayLiteral

https://doc.qt.io/qt-5/qbytearray.html#QByteArrayLiteral

QByteArray b = QByteArrayLiteral("\x12\x00\xa4\x42\x51\x00\x00\x99");