Hex to Ascii and Ascii to Hex Problem

[havoc]

hi all,
This is my code:

#include <QCoreApplication>
#include <QDebug>
QString HexToAscii(QString Str);
QString AsciiToHex(QString Str);

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

qDebug() << HexToAscii("4170706c65");
qDebug() << AsciiToHex(HexToAscii("4170706c65").toLocal8Bit());

qDebug() << HexToAscii("410070706c65"); // "00" is added after "41"
qDebug() << AsciiToHex(HexToAscii("410070706c65").toLocal8Bit());

return a.exec();
}


QString HexToAscii(QString String)

{

QByteArray ByteArray1=String.toUtf8();

const char* chArr1=ByteArray1.constData();

QByteArray ByteArray2=QByteArray::fromHex(chArr1);

const char* chArr2=ByteArray2.constData();

return QString::fromUtf8(chArr2);

}


QString AsciiToHex(QString String)

{

QByteArray ByteArray1=String.toUtf8();

QByteArray ByteArray2=ByteArray1.toHex();

const char* chArr1=ByteArray2.constData();

return QString::fromUtf8(chArr1);

}

And the Output is:
"Apple"
"4170706c65"
"A"
"41"


why the "00" is causing the problem there? I want the last line to be "410070706c65"
Sorry but I'm very new to Qt, please help me with the solution and the reason behind the unexpected value.
thanks in advance.

[Santosh Reddy]

Please specify the platform/Qt Veriosn/ABI (32/64/... bit) information.

[ChrisW67]

why the "00" is causing the problem there? I want the last line to be "410070706c65"
Sorry but I'm very new to Qt, please help me with the solution and the reason behind the unexpected value.
thanks in advance.
C-strings are terminated by NUL (i.e. '\0') character (nothing to do with Qt). Feeding an array of bytes contain zeroes to any function expecting a C-string (i.e. const char *) will behave this way: this includes the Qt function QString::fromUtf8().

QByteArray is the Qt data type that handles arrays of arbitrary bytes. Your HexToAscii() function is what QByteArray::fromHex() does. Your AsciiToHex() is precisely what QByteArray::toHex() does. All the other stuff you do in those functions is unnecessary and ultimately breaks your expectations.

[havoc]

thanks you for your responses. ChrisW67, can you show me an example on how I can deal with the NUL? I am basically wanting it for a program which writes(using socket->write() ) the data containing NUL somewhere in the middle of the string, often many NULs inbetween. How can I manage it?

[ChrisW67]

You use the version of QIODevice::write() that takes a QByteArray or a const char * with a size, and not the version that expects a nul terminated c string. None of this has anything to do with converting bytes to or from hexadecimal.

[havoc]

Thank you, I'll look onto that. Actually the packet data I am trying to send is like the ASCII form of "02000204690001000001" and its hard for me to directly send the packet in ASCII form so I was trying to store the packet in hexadecimal form in a variable and use it at the time of sending by converting it to ASCII using the HexToAscii converter and later after receiving the bytes in ASCII form I want to display them in Hex form using the AsciiToHex converter. I have done this easily in Visual Basic 6 and I recently started learning Qt so I'm facing too many problems. I searched many times still found nothing. I don't know if I'm asking for too much, but can you give me a clue or any link where I can learn this from?

[ChrisW67]

Actually the packet data I am trying to send is like the ASCII form of "02000204690001000001"
What do you mean "the ASCII form of" in relation to a perfectly good ASCII string?

I think you more urgently need to understand what hexadecimal is: it is a human-readable representation of a number in base 16. A hexadecimal string is an ASCII string representing a collection of bytes that may not have values valid in an ASCII string, i.e. any byte value over 127, or inconvenient in a string like zero bytes.


Assuming that string is in a QString variable s:


QByteArray buf = s.toLatin1();
iodev.write( buf );

Will send that string through the device. That is a series of 20 bytes with values (decimal): 48 50 48 48 48 50 etc.

If you mean the string is the hexadecimal representation of a series of 10 bytes then:


QByteArray buf = QByteArray::fromHex( s.toLatin1() );
iodev.write( buf );

Will write ten bytes with the values (decimal): 2 0 2 4 105 0 1 0 0 1

There is no need to convert binary data to hexadecimal strings in Qt unless you are doing it to display to a human.