How to input hex value to QByteArray efficient ?

Hiloshi

Dear All,

I want to input hex value into QByteArray, below is my code:

 QByteArray header;
 header = header.append(0x38);
 header = header.append(0x39);
 header = header.toHex();

As you see I have to input each value one by one, cannot direct input a series of number.
For example, I cannot define header[0x38,0x39,0x42,0x01,0xA8] in one code.
Is my above method correct ? Is there any better way to input hex data directly ?

Thanks,

jsulm

@Hiloshi Using C++11 you can do:

QByteArray header{0x38,0x39,0x42,0x01,0xA8};

Hiloshi

Dear @jsulm ,

It is not working in my project, I suspect my project is not C++ 11 ??
The error message is:

no matching function for call to ‘QByteArray::QByteArray(<brace-enclosed initializer list>)’
     QByteArray header{0x38,0x39,0x42,0x01,0xA8};
                                               ^

My compiler is "~/rpi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-g++". Is it support C++ 11 ?

Thanks,

jsulm

@Hiloshi Please call your compiler with -v parameter to get the version.
Also you probably have to activate C++11 first in pro file:

CONFIG += c++11

J.Hilk

@Hiloshi I don't think you can initialize a QBytrArray in that way.

this however should work:

QList<int> l{0xFE,0x64,0x01};
QByteArray bArray;
for(int i =0; i< l.size(); i++)
    bArray[i] = l[i];

mpergand

C++11 you can do:
QByteArray header{0x38,0x39,0x42,0x01,0xA8};

No, it's not working in C++14 either.

This seems to work:

unsigned char dat[]={0x38,0x39,0x42,0x01,0xA8};
QByteArray hex=QByteArray::fromRawData((char*)dat,5);
qDebug()<<hex.toHex();

Annoying error with unsigned char, requiring a cast ...
(it's clearly explained in the doc, but they use const char that produce an error for me)

? Offline

You can also follow one of these three ways:

QByteArray ba1{"\x38\x39\x42\x01\xA8"}; 
QByteArray ba2 = QByteArrayLiteral("\x38\x39\x42\x01\xA8");
Stuff::ByteArray ba3{0x38,0x39,0x42,0x01,0xA8};

ba1 is constructed from a C-style string literal using QByteArray::QByteArray(const char *data, int size = -1). ba2 is probably the most efficient, see QStringLiteral explained and Qt Weekly #13: QStringLiteral. For ba3 we use a small helper class that extends QByteArray:

namespace Stuff
{
    struct ByteArray: public QByteArray
    {
        ByteArray(std::initializer_list<unsigned char> lst)
            : QByteArray(reinterpret_cast<char const *>(lst.begin()), lst.size())
        {}
    };
}

jsulm

@J.Hilk @mpergand Yes, looks like it is not supported

Hiloshi

Thank you all.

if only add CONFIG += c++11:

QByteArray Testdate{0x41,0x42};
qDebug()<<"Testdata="<<Testdate;
//then result is
Testdata= "BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB"

Use QList, QByteArray::fromRawData and @Wieland 's three approach could input hex value to QByteArray successfully.

I should try to understand what is C++11 and read Qt Weekly #13: QStringLiteral in more detail.

Thanks again.

? Offline

@Hiloshi said in How to input hex value to QByteArray efficient ?:

QByteArray Testdate{0x41,0x42};
qDebug()<<"Testdata="<<Testdate;
//then result is
Testdata= "BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB"

Because QByteArray Testdate{0x41,0x42}; calls this constructor: QByteArray::QByteArray(int size, char ch) with size=0x41=65 and ch=0x42='B'.

See QByteArray Class:

Constructs a byte array of size size with every byte set to character ch.

oPryzeLP

Alternatively, you can use QByteArray::fromHex()

QByteArray header = QByteArray::fromHex("38394201a8");