MOC Bug?

kDohmen

Hello,

I was asking myselfe if this is a bug:

namespace somenamespacename
{
#ifdef Q_OS_LINUX
  class myErrClass : public QObject
  {
  Q_OBJECT

  public:
    myClass();
  signals:
    void mySignal();
  }
#endif

  class mySecClass : public QObject
  {
  Q_OBJECT

  public:
    mySecClass();
  signals:
    void mySecSignal();
  }
}

Assuming i have implemented all functions in the cpp I get an error of undefined references for myErrClass. Looking in the moc file I saw that qmake did not created the moc-content for myErrClass.

If I remove the ifdef the content is created and everything is as expected.

sierdzio

Do you get the errors when Q_OS_LINUX is defined or not? Or do you get them always? Are the myErrClass functions also ifdeffed in the source file?

kDohmen

I get the error when Q_OS_LINUX is defined (compiling on Debian 7). The functions are also ifdeffed in the source file.

sierdzio

OK, I've checked now and although it is not mentioned in the official MOC documentation, this tool has trouble understanding any ifdefs.

See: "link":http://stackoverflow.com/questions/4246533/qt-signal-wrapped-in-an-ifdef and "link":http://grokbase.com/t/gg/android-qt/129q8e9fem/moc-doesnt-see-ifndef-android-guards.

kDohmen

so no bug, just not featured... ok, then I need to do a workaround... thanks :)

sierdzio

I would put it more as "known issue" - but it's been there since the dawn of time and I don't remember anybody volunteering to fix it.

One of the problems I see is that MOC is run by qmake. But actual compilation flags are passed later - when the project is actually build. So implementing it properly in MOC is probably a big effort.

SGaist

Hi,

IIRC, that's a limitation of Qt 4's moc, the Qt 5 version should work better in that aspect.

kDohmen

I use Qt 5.3.2 so it is not only a limitation of Qt 4s moc.

SGaist

Just tested with your code as a base and the minor modifications it needed to build and got no error with Qt 5.4. Can you post a complete example that fails for you ?