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Qt-interest Archive, December 2006
Qt4.2.2's moc is mocked by digraph

Message 1 in thread

Hi

I think I found a bug in moc. I would like to explain the bug and I also have fixed the problem. Please tell me how can I send the patch for this problem.

I am new at this mailing list. A bug report should go to other place, please let me know. 

Environment: Qt4.2.2, SuSE Linux 10.1, gcc 4.1.0.

Could you please have a look at next code?
-----
#include <QObject>
namespace AAA {
  /** \class BaseA 
      This is almost nothing, but in the namesapace AAA.
   */ 
  class BaseA {
  public:
    BaseA(){}
    virtual ~BaseA(){}
  };
} // namesapace AAA

namespace BBB {
/** \class DerivedB 
*/
class DerivedB : public QObject, public ::AAA::BaseA {
  Q_OBJECT
public:
  DerivedB() : QObject(0), BaseA() {}
  virtual ~DerivedB() {}
public slots:
signals:
private:
};
} //namespace BBB
---

When you compile the code, you will get next errors from gcc.   

MocDigraphTrap.moc.cc: In member function `virtual void* BBB::DerivedB::qt_metacast(const char*)':
MocDigraphTrap.moc.cc:52: error: expected `<' before '[' token
MocDigraphTrap.moc.cc:52: error: expected identifier before '[' token
MocDigraphTrap.moc.cc:52: error: expected `>' before '[' token
MocDigraphTrap.moc.cc:52: error: expected `(' before '[' token
MocDigraphTrap.moc.cc:52: error: expected primary-expression before '[' token
MocDigraphTrap.moc.cc:52: error: expected primary-expression before ':' token
MocDigraphTrap.moc.cc:52: error: expected `]' before ':' token
MocDigraphTrap.moc.cc:52: error: expected `)' before ':' token
MocDigraphTrap.moc.cc:52: error: expected `;' before ':' token
MocDigraphTrap.moc.cc:52: error: expected primary-expression before ':' token
MocDigraphTrap.moc.cc:52: error: expected `;' before ':' token
-----

The error happens in the MocDigraphTrap.moc.cc:52, which is

  return static_cast<::AAA::BaseA*>(const_cast<DerivedB*>(this));

in the next function qt_metacast().

---
void *BBB::DerivedB::qt_metacast(const char *_clname)
{
    if (!_clname) return 0;
    if (!strcmp(_clname, qt_meta_stringdata_BBB__DerivedB))
	return static_cast<void*>(const_cast<DerivedB*>(this));
    if (!strcmp(_clname, "::AAA::BaseA"))
	return static_cast<::AAA::BaseA*>(const_cast<DerivedB*>(this));
    return QObject::qt_metacast(_clname);
}
---

The error said there is no token < before [. No such token you can see, I think. This is because ISO standard (1999) digraph. 
(see http://david.tribble.com/text/cdiffs.htm#C90-digraph)

I think C's Trigraph has enough bad reputation, but the digraph may be not yet. According to the standard, cpp must change '<:' to '['. So, you can not write std::vector<::some>. (In a template case, gcc gives us really useful error message, but the cast case is not.) Qt4's moc may not consider this situation.
 
But actually, if you zap the src/tools/moc/generator.cpp, some of the reinterpred_cast knows this problem. I do not see why the writer did not put a space to static_cast....

Anyway, this bug is easy to fix, can I put my patch for src/tools/moc/generate.cpp to here?

Thank you!

Gruesse,
Hitoshi Yamauchi
-- 
 [ signature omitted ]
Message 2 in thread

On 12/16/06, hito111@xxxxxx <hito111@xxxxxx> wrote:
> Hi
>
> I think I found a bug in moc. I would like to explain the bug and I also have fixed the problem. Please tell me how can I send the patch for this problem.

Great for finding both the bug and solution.

> I am new at this mailing list. A bug report should go to other place, please let me know.

They should go directly to Trolltech, qt-bugs (at) trolltech.com.

-- 
 [ signature omitted ]
Message 3 in thread

Hi,

Von: "Robin Ericsson"
> On 12/16/06, hito111@xxxxxx <hito111@xxxxxx> wrote:
> > I think I found a bug in moc. I would like to explain the bug and I also
> have fixed the problem. Please tell me how can I send the patch for this
> problem.
> 
> Great for finding both the bug and solution.
> 
> > I am new at this mailing list. A bug report should go to other place,
> please let me know.
> 
> They should go directly to Trolltech, qt-bugs (at) trolltech.com.

Thanks! I will send this to qt-bugs.

Best Regards,
Hitoshi Yamauchi
-- 
 [ signature omitted ]
Message 4 in thread

On Saturday 16 December 2006 21:57, hito111@xxxxxx wrote:
> Hi
>
> I think I found a bug in moc. I would like to explain the bug and I also
> have fixed the problem. Please tell me how can I send the patch for this
> problem.
>
> I am new at this mailing list. A bug report should go to other place,
> please let me know.
>
> Environment: Qt4.2.2, SuSE Linux 10.1, gcc 4.1.0.
>
> Could you please have a look at next code?
> -----
> #include <QObject>
> namespace AAA {
>   /** \class BaseA
>       This is almost nothing, but in the namesapace AAA.
>    */
>   class BaseA {
>   public:
>     BaseA(){}
>     virtual ~BaseA(){}
>   };
> } // namesapace AAA
>
> namespace BBB {
> /** \class DerivedB
> */
> class DerivedB : public QObject, public ::AAA::BaseA {
>   Q_OBJECT
> public:
>   DerivedB() : QObject(0), BaseA() {}
>   virtual ~DerivedB() {}
> public slots:
> signals:
> private:
> };
> } //namespace BBB
> ---
>
> When you compile the code, you will get next errors from gcc.
>
> MocDigraphTrap.moc.cc: In member function `virtual void*
> BBB::DerivedB::qt_metacast(const char*)': MocDigraphTrap.moc.cc:52: error:
> expected `<' before '[' token
> MocDigraphTrap.moc.cc:52: error: expected identifier before '[' token
> MocDigraphTrap.moc.cc:52: error: expected `>' before '[' token
> MocDigraphTrap.moc.cc:52: error: expected `(' before '[' token
> MocDigraphTrap.moc.cc:52: error: expected primary-expression before '['
> token MocDigraphTrap.moc.cc:52: error: expected primary-expression before
> ':' token MocDigraphTrap.moc.cc:52: error: expected `]' before ':' token
> MocDigraphTrap.moc.cc:52: error: expected `)' before ':' token
> MocDigraphTrap.moc.cc:52: error: expected `;' before ':' token
> MocDigraphTrap.moc.cc:52: error: expected primary-expression before ':'
> token MocDigraphTrap.moc.cc:52: error: expected `;' before ':' token
> -----
>
> The error happens in the MocDigraphTrap.moc.cc:52, which is
>
>   return static_cast<::AAA::BaseA*>(const_cast<DerivedB*>(this));
>
> in the next function qt_metacast().
>
> ---
> void *BBB::DerivedB::qt_metacast(const char *_clname)
> {
>     if (!_clname) return 0;
>     if (!strcmp(_clname, qt_meta_stringdata_BBB__DerivedB))
> 	return static_cast<void*>(const_cast<DerivedB*>(this));
>     if (!strcmp(_clname, "::AAA::BaseA"))
> 	return static_cast<::AAA::BaseA*>(const_cast<DerivedB*>(this));
>     return QObject::qt_metacast(_clname);
> }
> ---
>
> The error said there is no token < before [. No such token you can see, I
> think. This is because ISO standard (1999) digraph. (see
> http://david.tribble.com/text/cdiffs.htm#C90-digraph)
>
> I think C's Trigraph has enough bad reputation, but the digraph may be not
> yet. According to the standard, cpp must change '<:' to '['. So, you can
> not write std::vector<::some>. (In a template case, gcc gives us really
> useful error message, but the cast case is not.) Qt4's moc may not consider
> this situation.
>
> But actually, if you zap the src/tools/moc/generator.cpp, some of the
> reinterpred_cast knows this problem. I do not see why the writer did not
> put a space to static_cast....
>
> Anyway, this bug is easy to fix, can I put my patch for
> src/tools/moc/generate.cpp to here?
>
> Thank you!

Well spotted! Thanks a lot for the report. It'll be fixed in tomorrow's 
4.2/4.3 snapshots.


Simon

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