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moc



SYNOPSIS

       moc  [-o  file] [-i] [-f] [-k] [-ldbg] [-nw] [-p path] [-q
       path] [-v] file


DESCRIPTION

       This page documents the Meta Object Compiler  for  the  Qt
       GUI  application  framework. The moc reads one or more C++
       class declarations from a C++ header or  source  file  and
       generates  one  C++  source  file  containing  meta object
       information for the classes. The C++ source file generated
       by   the   moc  must  be  compiled  and  linked  with  the
       implementation of the class (or it can be  #included  into
       the class's source file).

       If  you  use  qmake  to create your Makefiles, build rules
       will be included that call the moc when required,  so  you
       will not need to use the moc directly.

       In brief, the meta object system is a structure used by Qt
       (see http://doc.trolltech.com) for  component  programming
       and  run  time  type  information.  It adds properties and
       inheritance information to (some) classes and  provides  a
       new type of communication between those instances of those
       classes, signal-slot connections.


OPTIONS

       -o file
              Write output to file rather than to stdout.

       -f     Force the generation of an  #include  statement  in
              the  output.   This  is the default for files whose
              name  matches  the  regular  expression  .[hH][^.]*
              (i.e.  the  extension  starts  with  H or h ). This
              option is only useful if you have header files that
              do not follow the standard naming conventions.

       -i     Do  not  generate  an  #include  statement  in  the
              output.  This may be used to run moc on a C++  file
              containing  one  or  more  class  declarations. You
              should then #include the meta object  code  in  the
              .cpp file (see USAGE below).  If both -f and -i are
              present, the last one wins.

       -nw    Do not generate any warnings. Not recommended.

       -ldbg  Write a flood of lex debug information to stdout.

       -p path
              Makes moc prepend path/ to the  file  name  in  the
              generated #include statement (if one is generated).

       -q path
       moc is almost always invoked by make(1), not by hand.

       moc  is typically used with an input file containing class
       declarations like this:

           class YourClass : public QObject {
               Q_OBJECT
               Q_PROPERTY( ... )
               Q_CLASSINFO( ... )

           public:
               YourClass( QObject * parent=0, const char * name=0 );
               ~YourClass();

           signals:

           public slots:

           };

       Here is a useful makefile rule if you only use GNU make:

           m%.cpp: %.h
                   moc $< -o $@

       If you want to write  portably,  you  can  use  individual
       rules of the following form:

           mNAME.cpp: NAME.h
                   moc $< -o $@

       You  must  also  remember to add mNAME.cpp to your SOURCES
       (substitute your favorite name) variable  and  mNAME.o  to
       your OBJECTS variable.

       (While  we  prefer  to name our C++ source files .cpp, the
       moc doesn't know that, so you can use .C, .cc,  .CC,  .cxx
       or even .c++ if you prefer.)

       If  you have class declarations in C++ files, we recommend
       that you use a makefile rule like this:

           NAME.o: mNAME.cpp

           mNAME.cpp: NAME.cpp
                   moc -i $< -o $@

       This guarantees that make(1) will run the  moc  before  it
       compiles NAME.cpp.  You can then put

           #include "nNAME.cpp"

       The  moc  does  not  expand #include or #define, it simply
       skips any preprocessor directives it encounters.  This  is
       regrettable, but is normally not a problem in practice.

       The  moc  does not handle all of C++.  The main problem is
       that class templates cannot have signals or  slots.   This
       is an important bug.  Here is an example:

           class SomeTemplate<int> : public QFrame {
               Q_OBJECT
               ....
           signals:
               void bugInMocDetected( int );
           };

       Less  importantly,  the  following constructs are illegal.
       All of them have have  alternatives  which  we  think  are
       usually  better,  so  removing  these limitations is not a
       high priority for us.

   Multiple inheritance requires QObject to be first.
       If you are using multiple inheritance,  moc  assumes  that
       the first inherited class is a subclass of QObject.  Also,
       be sure that only the first inherited class is a  QObject.

           class SomeClass : public QObject, public OtherClass {
               ...
           };

       This  bug  is almost impossible to fix; since the moc does
       not expand #include or #define, it cannot find  out  which
       one of the base classes is a QObject.

   Function pointers cannot be arguments to signals or slots.
       In  most  cases  where  you  would consider that, we think
       inheritance is a better alternative.  Here is  an  example
       of illegal syntax:

           class SomeClass : public QObject {
               Q_OBJECT
               ...
           public slots:
               // illegal
               void apply( void (*apply)(List *, void *), void * );
           };

       You can work around this restriction like this:

           typedef void (*ApplyFunctionType)( List *, void * );

           class SomeClass : public QObject {
               Q_OBJECT

       public  sections  instead.   Here  is  an  example  of the
       illegal syntax:

           class SomeClass : public QObject {
               Q_OBJECT
               ...
           signals:
               friend class ClassTemplate<char>; // illegal
           };

   Signals and slots cannot be upgraded
       The C++ feature of upgrading an inherited member  function
       to  public  status  is  not  extended to cover signals and
       slots.  Here is an illegal example:

           class Whatever : public QButtonGroup {
               ...
           public slots:
               QButtonGroup::buttonPressed; // illegal
               ...
           };

       The QButtonGroup::buttonPressed() slot is protected.

       C++ quiz: What happens if you try to upgrade  a  protected
       member function which is overloaded?

              - All the functions are upgraded.

              - That is not legal C++.

   Type macros cannot be used for signal and slot arguments
       Since  the  moc  does not expand #define, type macros that
       take an argument will not work in signals and slots.  Here
       is an illegal example:

           #ifdef ultrix
           #define SIGNEDNESS(a) unsigned a
           #else
           #define SIGNEDNESS(a) a
           #endif
           class Whatever : public QObject {
               ...
           signals:
               void someSignal( SIGNEDNESS(int) ); // illegal
           };

       A #define without arguments works.

   Nested  classes cannot be in the signals or slots sections nor
       have signals or slots
       Here's an example:
           };

   Constructors cannot be used in signals or slots sections
       It is a mystery to us why anyone would put  a  constructor
       on  either  the  signals  or  slots  sections.  You can't,
       anyway (except that it happens to  work  in  some  cases).
       Put  them  in private, protected or public sections, where
       they belong.  Here is an example of the illegal syntax:

           class SomeClass : public QObject {
               Q_OBJECT
           public slots:
               SomeClass( QObject *parent, const char *name )
                   : QObject( parent, name ) {} // illegal
               ...
           };

   Properties need to be declared before the public section  that
       contains the respective get and set functions
       Declaring  the  first  property within or after the public
       section  that  contains  the  type  definition   and   the
       respective   get  and  set  functions  does  not  work  as
       expected. The moc will complain that it can  neither  find
       the  functions nor resolve the type. Here is an example of
       the illegal syntax:

           class SomeClass : public QObject {
               Q_OBJECT
           public:
               ...
               // illegal
               Q_PROPERTY( Priority priority READ priority WRITE setPriority )
               Q_ENUMS( Priority )
               enum Priority { High, Low, VeryHigh, VeryLow };
               void setPriority( Priority );
               Priority priority() const;
               ...
           };

       Work around this limitation by declaring all properties at
       the  beginning  of  the  class  declaration,  right  after
       Q_OBJECT:

           class SomeClass : public QObject {
               Q_OBJECT
               Q_PROPERTY( Priority priority READ priority WRITE setPriority )
               Q_ENUMS( Priority )
           public:
               ...
               enum Priority { High, Low, VeryHigh, VeryLow };
               void setPriority( Priority );

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