Qdebug display hex value

Question

I am trying to display a number using QDebug in the Hex format. Below is the code which I have written. It is working but the output has string contents enclosed in double quotes:

How to remove these quotes?

m_CanMsg_ptr->id = 0x720;
m_CanMsg_ptr->sizeData = 1;
m_CanMsg_ptr->data[0] = 0x05;

MessageID.setNum(m_CanMsg_ptr->id,16);
DataSize  = QString("%1").arg(m_CanMsg_ptr->sizeData, 0, 16);
data      = QString("%1").arg(m_CanMsg_ptr->data[0], 0, 16)

qDebug() << "Heart-Beat : Msg ID = " << MessageID << "  Msg DLC = " << DataSize;
qDebug() << "Msg Data " << " = " << data;

I did as per these resources:

http://forum.qt.io/topic/5003/moved-how-to-display-a-local-variable-in-hex-when-debugging-a-qt-app/2 http://qt.shoutwiki.com/wiki/Convert_hexadecimal_to_decimal_and_vice-versa_in_Qt

Stowaway

Did you try using the + Operator instead of << for concatenating the strings? – Nocturnal

tried this but problem is half solved .... but yet full string is displayed with quotes .. ? How to remove this quotes – Stowaway

i get following output with quotes after replacing << with + .. "Heart-Beat : Msg ID = 720 Msg DLC = 1" – Stowaway

You remove quotes by using qDebug().noquote() – Shaquitashara

Answer 1

qDebug is a debug interface. It's not meant for custom-formatted output, it's simply a way of quickly getting data in readable form. It's meant for a developer, and the quotes are there to remind you that you've output a string. qDebug() presumes that the const char* data is a message and shows it without quotes, other string types like QString are "just data" and are shown with quotes.

If you want custom formatting, don't use qDebug(), use QTextStream:

#include <QTextStream>
#include <cstdio>

QTextStream out(stdout);

void f() {
   out << "Heart-Beat : Msg ID = " << MessageID << "  Msg DLC = " << DataSize << endl;
}

Omalley

Completeness it might be good to add: out << std::hex << MessageID << ... – Escalator

out is not an std::ostream, so std::hex won’t compile. But hex all by itself will (it’s Qt’s, not std’s). – Needless

The correct(?) way in Qt is Qt::hex(out) << number; or even Qt::showBase(Qt::hex(out)) << number; Or, for better readability IMHO: Qt::showbase(Qt::uppercasedigits(Qt::hex(out))) << number; – Cilia

Sadly, to get what want, I needed: out << "0x" << QString("%1").arg(number, 8, 16, QLatin1Char('0')).toUpper(); Which just looks ugly. But it seems the simplest that gives me the same as printf("0x%08X", number); – Cilia

@JesseChisholm Unfortunately, "streaming" string formatting was a failed STL experiment. Modern string fromatting eschews that old interface, and comes back to printf-like API in modern C++. But that's not in Qt yet. – Needless

@UnslanderMonica I suppose this would be always a point of debate (also, new interface is nothing like printf). The problem of format string output is its fragility to usage, portability OR high cost, choose two of those. Problem of stl-like implementation was its annoying "I toggle it once and untoggle after" approach to output modes, but supposedly it had to generate a compile time , static sequence of operations upon stream, no excess memory allocation, stack crawling and parsing a string, no dependency on the actual types of arguments changing from platform to platform. – Kirstinkirstyn

Answer 2

The solution is simple:

#include <QDebug>

int value = 0x12345;
qDebug() << "Value : " << hex << value;

Gesso

"Furthermore, QTextStream manipulators can be piped into a QDebug stream." -- doc.qt.io/qt-5/qdebug.html#formatting-options – Bifilar

QTextStream also defines several global manipulator functions – Bifilar

It should be noted that if the value is a char, this will not work, but can be easily resolved by casting the char to an int which then makes it work. – Escalator

As of Qt 5.14, hex is exposed through the Qt namespace, Qt::hex, and you can use it with and without the Qt:: prefix. As of Qt 5.15, hex is deprecated and Qt::hex is the preferred usage. – Ka

To show the 0x prefix, use Qt::hex << Qt::showbase << your_value – Tundra

Answer 3

You could format string first:

int myValue = 0x1234;
QString valueInHex= QString("%1").arg(myValue , 0, 16);
qDebug() << "value = " << valueInHex;

Divulgence

Answer 4

Another way of doing this would be:

int value = 0xFFFF;
qDebug() << QString::number(value, 16);

Hope this helps.

Edit: To remove the quotes you can cast the number as a pointer, as qt will format that without using quotes. For instance:

int value = 0xFFFF;
qDebug() << (void *) value;  

Slightly hackish, but it works.

Mundell

+1 for being more efficient than qDebug() << QByteArray(...) (that produces a QString internally), but this too does not answer OP's question on how to get rid of the quotes. – Carnarvon

I must have missed that, I updated my answer with something that will remove quotes. – Mundell

Use noquote(), as in: qDebug().noquote() << QString::number(value, 16); – Ka

Answer 5

If one is not tied to use streaming operators, can go with the plain old %x and use qDebug with formatting string:

int hexnum = 0x56;
qDebug("My hex number is: %x", hexnum);

which will yield "My hex number is: 56", without quotes.

Vinegary

FYI, this implies that hexnum is unsigned – Breeder

Answer 6

qDebug() << QByteArray::number(myNumber).toHex()

Aronarondel

This does not remove the quotes as asked. Also, this produces more internal overhead than necessary: QByteArray::number(myNumber) creates a QByteArray with the decimal representation which then needs a second step for converting to hex. Suggested improvement: qDebug() << QByteArray::number(myNumber,16). – Carnarvon

Answer 7

Use noquote() to avoid the quotation marks. As in:

qDebug().noquote() << QString::number(value, 16);

Ka

Answer 8

May be a little late, but in case someone needs this:

As statet in the answere by Kuber Ober, Qt only removes the quotes if it's a const char * passed to qDebug. However, Qt provides a macro to do the same with a QString - The qPrintable macro:

qDebug() << qPrintable(QString("String without quotes")) << QString("String with quotes");

This way, you can use the QString::number function (as provided by TheDancinZerg) to format the string:

int value = 0xFFFF;
qDebug() << qPrintable(QString::number(value, 16));

Smacking

Answer 9

int value = 0xff005542;
qDebug() << QString("%1").arg(value , 0, 16).toUpper();

>>> FF005542

That'll give you hex output at whatever length is required. But if you'd like fixed width output, this is handy (example of four hex digits):

int value = 0xff;
qDebug() << QString("%1").arg(value, 4, 16, (QChar)'0').toUpper();
//      Here's the fixed field length⬆︎

>>> 00FF

Revulsion

Answer 10

Just a note! The method using <<hex is deprecieted now, so it's recommended to use:

#include <QDebug>

int num = 0x4321;
qDebug() << "Hex num: " <<Qt::hex << num;

Because, if you compile this way just using <<hex you will got some warnings, what means that soon this form to write will not be compatible anymore. For more infos take a look at Qt documentation

Intendment

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. – Thersathersites

Answer 11

This is why you want to learn C before C++ & Qt:

qDebug("Data for test case 1: 0x%04X", crc)

Done, always works. No extra spaces, no extra quotes, no extra .noquote or << or ::hex or .toUpper etc.

Polysaccharide