trying to port an application to qt4.8 : qstring ambigous error

[cr3005]

hello

I have this little cool application, reveal, which is a exif metadata viewer. It is from 2006, coded with qt4. Apart from some minor adjustments, it compiles until

g++ -c -pipe -O2 -O2 -I/usr/include -D_REENTRANT -Wall -W -DBIN_DIR=\""/usr/bin\"" -DRESOURCE_DIR=\""/usr/share/Reveal\"" -DTARGET=\""Reveal\"" -DNEEDED_TRANSLATIONS=\""Reveal commonDialogs generalTools qt\"" -DQT_NO_DEBUG -DQT_XML_LIB -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtNetwork -I/usr/include/qt4/QtGui -I/usr/include/qt4/QtXml -I/usr/include/qt4 -Itmp -o tmp/dynamicSlider.o ../src/_commonWidgets/dynamicSlider.cpp
../src/_commonWidgets/dynamicSlider.cpp: In member function 'void DynamicSlider::setPrefix(QString)':
../src/_commonWidgets/dynamicSlider.cpp:54:27: error: call of overloaded 'QString(NULL)' is ambiguous
/usr/include/qt4/QtCore/qstring.h:428:43: note: candidates are: QString::QString(const QByteArray&)
/usr/include/qt4/QtCore/qstring.h:426:43: note:                 QString::QString(const char*)
/usr/include/qt4/QtCore/qstring.h:727:8: note:                 QString::QString(const QString&)
/usr/include/qt4/QtCore/qstring.h:106:5: note:                 QString::QString(QChar)
/usr/include/qt4/QtCore/qstring.h:105:14: note:                 QString::QString(const QChar*)
../src/_commonWidgets/dynamicSlider.cpp: In member function 'void DynamicSlider::setSuffix(QString)':
../src/_commonWidgets/dynamicSlider.cpp:68:27: error: call of overloaded 'QString(NULL)' is ambiguous
/usr/include/qt4/QtCore/qstring.h:428:43: note: candidates are: QString::QString(const QByteArray&)
/usr/include/qt4/QtCore/qstring.h:426:43: note:                 QString::QString(const char*)
/usr/include/qt4/QtCore/qstring.h:727:8: note:                 QString::QString(const QString&)
/usr/include/qt4/QtCore/qstring.h:106:5: note:                 QString::QString(QChar)
/usr/include/qt4/QtCore/qstring.h:105:14: note:                 QString::QString(const QChar*)
make: *** [tmp/dynamicSlider.o] Error 1

g++ -c -pipe -O2 -O2 -I/usr/include -D_REENTRANT -Wall -W -DBIN_DIR=\""/usr/bin\"" -DRESOURCE_DIR=\""/usr/share/Reveal\"" -DTARGET=\""Reveal\"" -DNEEDED_TRANSLATIONS=\""Reveal commonDialogs generalTools qt\"" -DQT_NO_DEBUG -DQT_XML_LIB -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtNetwork -I/usr/include/qt4/QtGui -I/usr/include/qt4/QtXml -I/usr/include/qt4 -Itmp -o tmp/dynamicSlider.o ../src/_commonWidgets/dynamicSlider.cpp
../src/_commonWidgets/dynamicSlider.cpp: In member function 'void DynamicSlider::setPrefix(QString)':
../src/_commonWidgets/dynamicSlider.cpp:54:27: error: call of overloaded 'QString(NULL)' is ambiguous
/usr/include/qt4/QtCore/qstring.h:428:43: note: candidates are: QString::QString(const QByteArray&)
/usr/include/qt4/QtCore/qstring.h:426:43: note:                 QString::QString(const char*)
/usr/include/qt4/QtCore/qstring.h:727:8: note:                 QString::QString(const QString&)
/usr/include/qt4/QtCore/qstring.h:106:5: note:                 QString::QString(QChar)
/usr/include/qt4/QtCore/qstring.h:105:14: note:                 QString::QString(const QChar*)
../src/_commonWidgets/dynamicSlider.cpp: In member function 'void DynamicSlider::setSuffix(QString)':
../src/_commonWidgets/dynamicSlider.cpp:68:27: error: call of overloaded 'QString(NULL)' is ambiguous
/usr/include/qt4/QtCore/qstring.h:428:43: note: candidates are: QString::QString(const QByteArray&)
/usr/include/qt4/QtCore/qstring.h:426:43: note:                 QString::QString(const char*)
/usr/include/qt4/QtCore/qstring.h:727:8: note:                 QString::QString(const QString&)
/usr/include/qt4/QtCore/qstring.h:106:5: note:                 QString::QString(QChar)
/usr/include/qt4/QtCore/qstring.h:105:14: note:                 QString::QString(const QChar*)
make: *** [tmp/dynamicSlider.o] Error 1

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where the file looks like this:

void DynamicSlider::setPrefix( QString val )
{
  prefix1 = val;
  prefix2 = QString( NULL );
  updateTooltipLabel();
}
//==========================================
void DynamicSlider::setPrefixes( QString v1, QString v2 )
{
  prefix1 = v1;
  prefix2 = v2;
  updateTooltipLabel();
}
//==========================================
void DynamicSlider::setSuffix( QString val )
{
  suffix1 = val;
  suffix2 = QString( NULL );
  updateTooltipLabel();
}

void DynamicSlider::setPrefix( QString val )
{
  prefix1 = val;
  prefix2 = QString( NULL );
  updateTooltipLabel();
}
//==========================================
void DynamicSlider::setPrefixes( QString v1, QString v2 )
{
  prefix1 = v1;
  prefix2 = v2;
  updateTooltipLabel();
}
//==========================================
void DynamicSlider::setSuffix( QString val )
{
  suffix1 = val;
  suffix2 = QString( NULL );
  updateTooltipLabel();
}

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and .h

///set two prefix values, one for when the value is positive and one for when the value is negative.
  void setPrefixes( QString prefix1, QString prefix2 );
 
  ///set the suffix that is displayed after the current slider value
  void setSuffix( QString val );
 
  ///set two suffix values, one for when the value is positive and one for when the value is negative.
  void setSuffixes( QString suffix1, QString suffix2 );

///set two prefix values, one for when the value is positive and one for when the value is negative.
  void setPrefixes( QString prefix1, QString prefix2 );

  ///set the suffix that is displayed after the current slider value
  void setSuffix( QString val );
  
  ///set two suffix values, one for when the value is positive and one for when the value is negative.
  void setSuffixes( QString suffix1, QString suffix2 );

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Now, with qt4.7, when I delete the NULL, it compiles through and runs.

With qt 4.8, I get a segmentation fault, gdb tells it faults in Qstring::fromLocal8Bit(char const*, int) ()

I am not familiar with qt, could somebody help me out?

thx in advance

[amleto]

just replace

QString(NULL)

with

""


e.g.

suffix2 = "";

suffix2 = "";

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[anda_skoa]

Just replace QString( NULL ) with QString() or call the string variable's clear() method.

Cheers,
_

[cr3005]

just replace

QString(NULL)

with

""


e.g.

suffix2 = "";

suffix2 = "";

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hmm, nope, just keeps segfaulting...

---

Added after 6 minutes:

Just replace QString( NULL ) with QString()

Cheers,
_

As I stated in my beginning post, I DID replace QString( NULL ) with QString() and it compiled through, but it segfaults with 4.8...
0x00007ffff5eb5b40 in Qstring::fromLocal8Bit(char const*, int) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4

or call the string variable's clear() method.

will try that, if I find out how...

[amleto]

sounds like maybe you have got too many Qt installs are are mixing up library binaries?

but since you have a runtime error, the issue is not likely to be syntax problem... More probable is data/value problem. Since you didnt show how that segfault is traced from your code, you are not making things easy to diagnose.