cannot convert argument 1 from 'QWidget *' to 'QObject *'

Alcor

Please bear with me and let me explain my problem.

I have a piece of code that uses QSyntaxHighlighter Class ( https://doc.qt.io/qt-5.15/qsyntaxhighlighter.html#QSyntaxHighlighter)

In the code, a class named GlslHighlighter is defined in glslHighlighter.h as follows:

class GlslHighlighter: public QSyntaxHighlighter
{
public:

    GlslHighlighter();
    virtual ~GlslHighlighter();

    void setDocument(
        QTextDocument *textdoc
    ,   const e_GlslLanguageType language);

.............

}

constructor in glslHighlighter.cpp is as follows:

GlslHighlighter::GlslHighlighter()
:   QSyntaxHighlighter(static_cast<QWidget*>(NULL))
,   m_language(GLSLT_Common)
{
}

Now, the constructor for QSyntaxHighlighter in Qt documentation is defined as follows:

QSyntaxHighlighter::QSyntaxHighlighter(QTextDocument *parent)

QSyntaxHighlighter::QSyntaxHighlighter(QObject *parent)

( https://doc.qt.io/qt-5.15/qsyntaxhighlighter.html#QSyntaxHighlighter-1)

Even in Qt4 documentation it is as follows:

QSyntaxHighlighter::QSyntaxHighlighter ( QObject * parent )

QSyntaxHighlighter::QSyntaxHighlighter ( QTextDocument * parent )

QSyntaxHighlighter::QSyntaxHighlighter ( QTextEdit * parent )

(https://het.as.utexas.edu/HET/Software/html/qsyntaxhighlighter.html#QSyntaxHighlighter)

When I am trying to compile GlslHighlighter.cpp, i get the error message as follows:

\glslhighlighter.cpp(40): error C2664: 'QSyntaxHighlighter::QSyntaxHighlighter(const QSyntaxHighlighter &)': cannot convert argument 1 from 'QWidget *' to 'QObject *'

Now, here is my doubt. Isn't argument 1 of the type QWidget* in violation of the definition of the constructor of the class GlslHighlighter? I don't see any way to fix this error without altering the argument type in the definition file ie glslHighlighter.h

J.Hilk

@Alcor your GlsHighlighter class is set up wrong, from the get go.

said in cannot convert argument 1 from 'QWidget *' to 'QObject *':

class GlslHighlighter: public QSyntaxHighlighter
{
public:
GlslHighlighter();
virtual ~GlslHighlighter();

void setDocument(
QTextDocument *textdoc
, const e_GlslLanguageType language);

.............
}

 class GlslHighlighter: public QSyntaxHighlighter
 {
      Q_OBJECT
 
public:
   GlslHighlighter(QObject *parent = nullptr);
   virtual ~GlslHighlighter();
 
 void setDocument(
     QTextDocument *textdoc
 ,   const e_GlslLanguageType language);
 
 .............
> }

in *.cpp

GlslHighlighter::GlslHighlighter(QObject *parent)
: QSyntaxHighlighter(parent)
, m_language(GLSLT_Common)
{
}

That fixes your issue, you don't need to modify any calling code and the now added Q_Object macro will prevent future pain and misery

Christian Ehrlicher

@Alcor since you pass a nullptr to the base class what's the problem to pass a QObject nullptr?

J.Hilk

@Alcor your GlsHighlighter class is set up wrong, from the get go.

said in cannot convert argument 1 from 'QWidget *' to 'QObject *':

class GlslHighlighter: public QSyntaxHighlighter
{
public:
GlslHighlighter();
virtual ~GlslHighlighter();

void setDocument(
QTextDocument *textdoc
, const e_GlslLanguageType language);

.............
}

 class GlslHighlighter: public QSyntaxHighlighter
 {
      Q_OBJECT
 
public:
   GlslHighlighter(QObject *parent = nullptr);
   virtual ~GlslHighlighter();
 
 void setDocument(
     QTextDocument *textdoc
 ,   const e_GlslLanguageType language);
 
 .............
> }

in *.cpp

GlslHighlighter::GlslHighlighter(QObject *parent)
: QSyntaxHighlighter(parent)
, m_language(GLSLT_Common)
{
}

That fixes your issue, you don't need to modify any calling code and the now added Q_Object macro will prevent future pain and misery

Alcor

@J-Hilk said in cannot convert argument 1 from 'QWidget *' to 'QObject *':

QObject *parent

Thank You. It worked.