Overloading QDebug in QtObject subclass

Tobias Fensch

Hello,
I want to debug out some information about a custom QtObject-subclass. Therefore I'm using the operator<< mechanism as described here.

This doesn't work for me.

My Test-Implementation:

DebugClass.h

#ifndef DEBUGCLASS_H
#define DEBUGCLASS_H

#include <QObject>

class DebugClass : public QObject
{
	Q_OBJECT
public:
	explicit DebugClass(QObject *parent = nullptr);

	int getX() const;

signals:

private:
	int x;
};

QDebug operator<< (QDebug , const DebugClass &);

#endif // DEBUGCLASS_H

DebugClass.cpp

#include "DebugClass.h"
#include <QDebug>

DebugClass::DebugClass(QObject *parent)
	: QObject{parent}
{
	x = 42;
}

QDebug operator<<(QDebug dbg, const DebugClass &info)
{
	dbg.nospace() << "This is x: " << info.getX();
	return dbg.maybeSpace();
}

int DebugClass::getX() const
{
	return x;
}

Using the DebugClass:

auto debugClass = new DebugClass();
qDebug() << "Test DebugClass:" << debugClass;

This gives me the following output:

"Test DebugClass: DebugClass(0x2af8d9e1250)"

The <<-Operator is never called.
Can someone help me with that?

thanks,
Tobias

kkoehne

@Tobias-Fensch said in Overloading QDebug in QtObject subclass:

"Test DebugClass: DebugClass(0x2af8d9e1250)"

The <<-Operator is never called.

It's not called because you pipe the pointer to your type, but the operator<<() expects a value (const reference) of your type.

To make C++ call your operator<<() make sure to de-reference the pointer.

jsulm

@Tobias-Fensch Did you put operator<< into a header file and did you include this header file where you are trying to use operator<<?

kkoehne

@Tobias-Fensch said in Overloading QDebug in QtObject subclass:

"Test DebugClass: DebugClass(0x2af8d9e1250)"

The <<-Operator is never called.

It's not called because you pipe the pointer to your type, but the operator<<() expects a value (const reference) of your type.

To make C++ call your operator<<() make sure to de-reference the pointer.