=head1 NAME moc - Qt meta object support code generator =head1 SYNOPSIS moc [options] [] ... =head1 DESCRIPTION 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). =head1 OPTIONS -o write output to file rather than stdout -I add dir to the include path for header files -E preprocess only; do not generate meta object code -D[=] define macro, with optional definition -U undefine macro -i do not generate an #include statement -p path prefix for included file -f[] force #include, optional file name -nn do not display notes -nw do not display warnings @ read additional options from file -v display version of moc =head1 EXIT STATUS moc returns 0 on success and other on unexcepted failure. =head1 BUGS 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 : 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. =head2 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. =head2 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 slots: void apply( ApplyFunctionType, char * ); }; It may sometimes be even better to replace the function pointer with inheritance and virtual functions, signals or slots. =head2 Friend declarations cannot be placed in signals or slots sections Sometimes it will work, but in general, friend declarations cannot be placed in signals or slots sections. Put them in the good old private, protected or public sections instead. Here is an example of the illegal syntax: class SomeClass : public QObject { Q_OBJECT ... signals: friend class ClassTemplate; // illegal }; =head2 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++. =head2 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. =head2 Nested classes cannot be in the signals or slots sections nor have signals or slots Here's an example: class A { Q_OBJECT public: class B { public slots: // illegal void b(); ... }; signals: class B { // illegal void b(); ... }: }; =head2 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 ... }; =head2 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 ); Priority priority() const; ... }; =head1 AUTHORS The Qt Company Ltd. Copyright (C) 2015 The Qt Company Ltd. Licensed through GNU Lesser General Public License/GNU General Public License.