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+.TH moc 1 "24 June 2001" "Trolltech AS" \" -*- nroff -*-
+.\"
+.\" $Id: qt/moc.1 3.3.4 edited May 27 2003 $
+.\"
+.\" Copyright 1992-2002 Trolltech AS. All rights reserved.
+.\"
+.\" This file is part of Qt and may be distributed and used according to
+.\" the terms and conditions described in the LICENSE file.
+.\"
+.nh
+.SH NAME
+moc \- generate Qt meta object support code
+.SH SYNOPSIS
+.B moc
+[\-o file] [\-i] [\-f] [\-k] [\-ldbg] [\-nw] [\-p path] [\-q path] [\-v] file
+.SH DESCRIPTION
+This page documents the
+.B Meta Object Compiler
+for the Qt GUI application framework. The
+.B 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
+.B moc
+must be compiled and linked with the implementation of the class (or it
+can be #included into the class's source file).
+.PP
+If you use
+.B qmake
+to create your Makefiles, build rules will be included that call the
+.B moc
+when required, so you will not need to use the
+.B moc
+directly.
+.PP
+In brief, the meta object system is a structure used by Qt (see
+.BR 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.
+.SH OPTIONS
+.TP
+.I "\-o file"
+Write output to
+.I file
+rather than to stdout.
+.TP
+.I \-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
+.B H
+or
+.B h
+). This
+option is only useful if you have header files that do not follow the
+standard naming conventions.
+.TP
+.I "\-i"
+Do not generate an #include statement in the output. This may be used
+to run
+.B 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
+.I \-f
+and
+.I \-i
+are present, the last one wins.
+.TP
+.I "\-nw"
+Do not generate any warnings. Not recommended.
+.TP
+.I "\-ldbg"
+Write a flood of lex debug information to stdout.
+.TP
+.I "\-p path"
+Makes
+.B moc
+prepend
+.IR path /
+to the file name in the generated #include statement (if one is generated).
+.TP
+.I "\-q path"
+Makes
+.B moc
+prepend
+.IR path /
+to the file name of qt #include files in the generated code.
+.TP
+.I "\-v"
+Displays the version of
+.B moc
+and Qt.
+.PP
+You can explicitly tell the
+.B moc
+not to parse parts of a header
+file. It recognizes any C++ comment (//) that contains the substrings
+MOC_SKIP_BEGIN or MOC_SKIP_END. They work as you would expect and you
+can have several levels of them. The net result as seen by the
+.B moc
+is as if you had removed all lines between a MOC_SKIP_BEGIN and a
+MOC_SKIP_END
+.SH USAGE
+.B moc
+is almost always invoked by
+.BR make (1),
+not by hand.
+.PP
+.B moc
+is typically used with an input file containing class declarations
+like this:
+.PP
+.in +4
+.nf
+class YourClass : public QObject {
+ Q_OBJECT
+ Q_PROPERTY( ... )
+ Q_CLASSINFO( ... )
+
+public:
+ YourClass( QObject * parent=0, const char * name=0 );
+ ~YourClass();
+
+signals:
+
+public slots:
+
+};
+.fi
+.in -4
+.PP
+Here is a useful makefile rule if you only use GNU make:
+.PP
+.in +4
+.nf
+m%.cpp: %.h
+ moc $< \-o $@
+.fi
+.in -4
+.PP
+If you want to write portably, you can use individual rules of the
+following form:
+.PP
+.in +4
+.nf
+mNAME.cpp: NAME.h
+ moc $< \-o $@
+.fi
+.in -4
+.PP
+You must also remember to add
+.I mNAME.cpp
+to your SOURCES (substitute your favorite name) variable and
+.I mNAME.o
+to your OBJECTS variable.
+.PP
+(While we prefer to name our C++ source files .cpp, the
+.B moc
+doesn't know that, so you can use .C, .cc, .CC, .cxx or even .c++ if
+you prefer.)
+.PP
+If you have class declarations in C++ files, we recommend that you use
+a makefile rule like this:
+.PP
+.in +4
+.nf
+NAME.o: mNAME.cpp
+
+mNAME.cpp: NAME.cpp
+ moc \-i $< \-o $@
+.fi
+.in -4
+.PP
+This guarantees that
+.BR make (1)
+will run the
+.B moc
+before it compiles
+.IR NAME.cpp .
+You can then put
+.PP
+.ti +4
+#include "nNAME.cpp"
+.PP
+at the end of
+.IR NAME.cpp ,
+where all the classes declared in that file are fully known.
+.SH DIAGNOSTICS
+Sometimes you may get linkage errors, saying that
+YourClass::className() is undefined or that YourClass lacks a vtbl.
+Those errors happen most often when you forget to compile the
+moc-generated C++ code or include that object file in the link
+command.
+.PP
+The
+.B moc
+will warn you about a number of dangerous or illegal constructs.
+.SH BUGS
+
+The
+.B 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
+.B 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:
+.PP
+.in +4
+.nf
+class SomeTemplate<int> : public QFrame {
+ Q_OBJECT
+ ....
+signals:
+ void bugInMocDetected( int );
+};
+.fi
+.in -4
+.PP
+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.
+.SS "Multiple inheritance requires QObject to be first."
+If you are using multiple inheritance,
+.B moc
+assumes that the
+.B first
+inherited class is a subclass of QObject. Also, be sure that
+.B only
+the first inherited class is a QObject.
+.PP
+.in +4
+.nf
+class SomeClass : public QObject, public OtherClass {
+ ...
+};
+.fi
+.in -4
+.PP
+This bug is almost impossible to fix; since the
+.B moc
+does not expand
+#include or #define, it cannot find out which one of the base classes is a
+QObject.
+.SS "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:
+.PP
+.in +4
+.nf
+class SomeClass : public QObject {
+ Q_OBJECT
+ ...
+public slots:
+ // illegal
+ void apply( void (*apply)(List *, void *), void * );
+};
+.fi
+.in -4
+.PP
+You can work around this restriction like this:
+.PP
+.in +4
+.nf
+typedef void (*ApplyFunctionType)( List *, void * );
+
+class SomeClass : public QObject {
+ Q_OBJECT
+ ...
+public slots:
+ void apply( ApplyFunctionType, char * );
+};
+.fi
+.in -4
+.PP
+It may sometimes be even better to replace the function pointer with
+inheritance and virtual functions, signals or slots.
+.SS "Friend declarations cannot be placed in signals or slots sections"
+Sometimes it will work, but in general, friend declarations cannot be
+placed in
+.B signals
+or
+.B slots
+sections. Put them in the good old
+.BR private ", " protected
+or
+.B public
+sections instead. Here is an example of the illegal syntax:
+.PP
+.in +4
+.nf
+class SomeClass : public QObject {
+ Q_OBJECT
+ ...
+signals:
+ friend class ClassTemplate<char>; // illegal
+};
+.fi
+.in -4
+.SS "Signals and slots cannot be upgraded"
+The C++ feature of upgrading an inherited member function to
+.B public
+status is not extended to cover signals and slots. Here is an illegal
+example:
+.PP
+.in +4
+.nf
+class Whatever : public QButtonGroup {
+ ...
+public slots:
+ QButtonGroup::buttonPressed; // illegal
+ ...
+};
+.fi
+.in -4
+.PP
+The QButtonGroup::buttonPressed() slot is protected.
+.PP
+C++ quiz: What happens if you try to upgrade a protected member
+function which is overloaded?
+.IP
+- All the functions are upgraded.
+.IP
+- That is not legal C++.
+.\" Good idea, but look in the SEE ALSO section...
+.SS "Type macros cannot be used for signal and slot arguments"
+
+Since the
+.B moc
+does not expand #define, type macros that take an argument
+will not work in signals and slots. Here is an illegal example:
+.PP
+.in +4
+.nf
+#ifdef ultrix
+#define SIGNEDNESS(a) unsigned a
+#else
+#define SIGNEDNESS(a) a
+#endif
+class Whatever : public QObject {
+ ...
+signals:
+ void someSignal( SIGNEDNESS(int) ); // illegal
+};
+.PP
+A #define without arguments works.
+.fi
+.in -4
+.SS "Nested classes cannot be in the signals or slots sections nor have signals or slots"
+Here's an example:
+.PP
+.in +4
+.nf
+class A {
+ Q_OBJECT
+public:
+ class B {
+ public slots: // illegal
+ void b();
+ ...
+ };
+signals:
+ class B { // illegal
+ void b();
+ ...
+ }:
+};
+.fi
+.in -4
+.PP
+.SS "Constructors cannot be used in signals or slots sections"
+It is a mystery to us why anyone would put a constructor on either the
+.B signals
+or
+.B slots
+sections. You can't, anyway (except that it happens to work in some
+cases). Put them in
+.BR private ", " protected
+or
+.B public
+sections, where they belong. Here is an example of the illegal syntax:
+.PP
+.in +4
+.nf
+class SomeClass : public QObject {
+ Q_OBJECT
+public slots:
+ SomeClass( QObject *parent, const char *name )
+ : QObject( parent, name ) {} // illegal
+ ...
+};
+.fi
+.in -4
+.SS "Properties need to be declared before the public section that contains the respective get and set functions"
+.PP
+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
+.B moc
+will complain that it can neither
+find the functions nor resolve the type. Here is an example of the
+illegal syntax:
+.PP
+.in +4
+.nf
+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;
+ ...
+};
+.fi
+.in -4
+.PP
+Work around this limitation by declaring all properties at the
+beginning of the class declaration, right after Q_OBJECT:
+.PP
+.in +4
+.nf
+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;
+ ...
+};
+.fi
+.in -4
+.PP
+.SH "SEE ALSO"
+.BR http://www.trolltech.com ", "
+.BR "C++ ARM, section r.11.3" " (for the answer to the quiz), and"
+.BR http://doc.trolltech.com " (for complete Qt documentation)."
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