How to convert ASCII Hex string to Byte array?

kahlenberg

Hi,
I try to convert a string, containing hex chars only, to a byte array. I could do it in C but in Qt I did not find any solution :) . Yes it is easy and trivial but really I need help.

Lets say I have a string like "E00200BA9EFC00AC", how can I convert it to an array like this:

bytearray[0]=0xE0
bytearray[1]=0x02
bytearray[2]=0x00
bytearray[3]=0xBA
....
bytearray[7]=0xAC

SGaist

Hi,

Do you mean something like QByteArray::fromHex ?

kahlenberg

@SGaist Thanks for answer, almost that. But it takes a QByteArray as parameter. I have a string. How can I convert a string to a QByteArray ? Every two character in my string represents a byte.

SGaist

Do you mean a std::string or "MyHexString" ?

kahlenberg

@SGaist QString MyHexString = "E00200BA9EFC00AC";

SGaist

Then why not do as the example in the doc suggests:

QByteArray myHexArray = QByteArray::fromHex("E00200BA9EFC00AC");

?

kahlenberg

@SGaist
Becausue fromHex accepts QByteArray as parameter, I have QString. Later I will get this string from UI element, QLineEdit
(ui->cmdToWrite->text(), this is QString)

QString MyHexString = "E00200BA9EFC00AC";
QByteArray cmd = QByteArray::fromHex(MyHexString);

Error message:
D:\Qt\Projects\Widget\mainwindow.cpp:40: error: no matching function for call to 'QByteArray::fromHex(QString&)'
QByteArray cmd = QByteArray::fromHex(MyHexString);
^

jduran_gm

@kahlenberg Take a look to this member function:

QByteArray QByteArray::fromHex(const QByteArray & hexEncoded)

Joaquim Duran

SGaist

Again, why create a QString ? Just use QByteArray directly or if you really really want a QString, use e.g. toLatin1

kahlenberg

@SGaist Oh, thank you very much, toLatin1() solved my problem. I didn't see it :) Thanks again.

rmk1842

@kahlenberg : could you post the code? I am in the same situation.

KroMignon

@rmk1842

QString MyHexString = "E00200BA9EFC00AC";
QByteArray cmd = QByteArray::fromHex(MyHexString);

You simply have to use QString::toLatin1():

QString MyHexString = "E00200BA9EFC00AC";
QByteArray cmd = QByteArray::fromHex(MyHexString.toLatin1());

fcarney

Like @SGaist said.
But QByteArray takes a string constant. I am using it is code right now. Extensively.

mganesh

      monitorCommand = "020400000006703B";
    QByteArray data_to_transmit = QByteArray::fromHex(monitorCommand.toUtf8());

qDebug() << monitorCommand << data_to_transmit;

it gives "020400000006703B for monitorcommond
for data_to_transmit "\x02\x04\x00\f\x00\x06\xB0""8"
but its not correctly converted to hex

Christian Ehrlicher

@mganesh This works fine for me. Your output can not match on what you've written. Please post all your test code

int main(int argc, char **argv)
{
  QCoreApplication app(argc, argv);
  QString monitorCommand = "020400000006703B";
  QByteArray data_to_transmit = QByteArray::fromHex(monitorCommand.toUtf8());
  qDebug() << monitorCommand << data_to_transmit;
  return 0;
}

-->
"020400000006703B" "\x02\x04\x00\x00\x00\x06p;"