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450 lines
10 KiB
450 lines
10 KiB
.TH moc 1 "24 June 2001" "Trolltech AS" \" -*- nroff -*-
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.\"
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.\" $Id: qt/moc.1 3.3.8 edited Jan 11 14:38 $
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.\"
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.\" Copyright (C) 1992-2007 Trolltech ASA. All rights reserved.
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.\"
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.\" This file is part of Qt and may be distributed and used according to
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.\" the terms and conditions described in the LICENSE file.
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.\"
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.nh
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.SH NAME
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moc \- generate Qt meta object support code
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.SH SYNOPSIS
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.B moc
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[-o file] [-i] [-f] [-k] [-ldbg] [-nw] [-p path] [-q path] [-v] file
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.SH DESCRIPTION
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This page documents the
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.B Meta Object Compiler
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for the Qt GUI application framework. The
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.B moc
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reads one or more C++ class declarations from a C++ header or source
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file and generates one C++ source file containing meta object
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information for the classes. The C++ source file generated by the
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.B moc
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must be compiled and linked with the implementation of the class (or it
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can be #included into the class's source file).
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.PP
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If you use
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.B qmake
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to create your Makefiles, build rules will be included that call the
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.B moc
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when required, so you will not need to use the
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.B moc
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directly.
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.PP
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In brief, the meta object system is a structure used by Qt (see
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.BR http://doc.trolltech.com ")"
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for component programming and run time type information. It adds
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properties and inheritance information to (some) classes and
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provides a new type of communication between those instances of those
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classes, signal-slot
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connections.
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.SH OPTIONS
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.TP
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.I "-o file"
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Write output to
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.I file
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rather than to stdout.
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.TP
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.I -f
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Force the generation of an #include statement in the output.
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This is the default for files whose name matches the regular
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expression .[hH][^.]* (i.e. the extension starts with
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.B H
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or
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.B h
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). This
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option is only useful if you have header files that do not follow the
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standard naming conventions.
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.TP
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.I "-i"
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Do not generate an #include statement in the output. This may be used
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to run
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.B moc
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on a C++ file containing one or more class declarations. You should then
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#include the meta object code in the .cpp file (see USAGE below). If both
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.I -f
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and
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.I -i
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are present, the last one wins.
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.TP
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.I "-nw"
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Do not generate any warnings. Not recommended.
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.TP
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.I "-ldbg"
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Write a flood of lex debug information to stdout.
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.TP
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.I "-p path"
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Makes
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.B moc
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prepend
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.IR path /
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to the file name in the generated #include statement (if one is generated).
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.TP
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.I "-q path"
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Makes
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.B moc
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prepend
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.IR path /
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to the file name of qt #include files in the generated code.
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.TP
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.I "-v"
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Displays the version of
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.B moc
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and Qt.
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.PP
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You can explicitly tell the
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.B moc
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not to parse parts of a header
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file. It recognizes any C++ comment (//) that contains the substrings
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MOC_SKIP_BEGIN or MOC_SKIP_END. They work as you would expect and you
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can have several levels of them. The net result as seen by the
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.B moc
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is as if you had removed all lines between a MOC_SKIP_BEGIN and a
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MOC_SKIP_END
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.SH USAGE
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.B moc
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is almost always invoked by
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.BR make (1),
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not by hand.
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.PP
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.B moc
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is typically used with an input file containing class declarations
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like this:
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.PP
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.in +4
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.nf
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class YourClass : public QObject {
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TQ_OBJECT
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Q_PROPERTY( ... )
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Q_CLASSINFO( ... )
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public:
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YourClass( QObject * parent=0, const char * name=0 );
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~YourClass();
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signals:
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public slots:
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};
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.fi
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.in -4
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.PP
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Here is a useful makefile rule if you only use GNU make:
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.PP
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.in +4
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.nf
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m%.cpp: %.h
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moc $< -o $@
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.fi
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.in -4
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.PP
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If you want to write portably, you can use individual rules of the
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following form:
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.PP
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.in +4
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.nf
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mNAME.cpp: NAME.h
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moc $< -o $@
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.fi
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.in -4
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.PP
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You must also remember to add
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.I mNAME.cpp
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to your SOURCES (substitute your favorite name) variable and
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.I mNAME.o
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to your OBJECTS variable.
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.PP
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(While we prefer to name our C++ source files .cpp, the
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.B moc
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doesn't know that, so you can use .C, .cc, .CC, .cxx or even .c++ if
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you prefer.)
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.PP
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If you have class declarations in C++ files, we recommend that you use
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a makefile rule like this:
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.PP
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.in +4
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.nf
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NAME.o: mNAME.cpp
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mNAME.cpp: NAME.cpp
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moc -i $< -o $@
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.fi
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.in -4
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.PP
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This guarantees that
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.BR make (1)
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will run the
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.B moc
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before it compiles
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.IR NAME.cpp .
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You can then put
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.PP
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.ti +4
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#include "nNAME.cpp"
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.PP
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at the end of
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.IR NAME.cpp ,
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where all the classes declared in that file are fully known.
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.SH DIAGNOSTICS
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Sometimes you may get linkage errors, saying that
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YourClass::className() is undefined or that YourClass lacks a vtbl.
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Those errors happen most often when you forget to compile the
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moc-generated C++ code or include that object file in the link
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command.
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.PP
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The
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.B moc
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will warn you about a number of dangerous or illegal constructs.
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.SH BUGS
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The
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.B moc
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does not expand #include or #define, it simply skips any preprocessor
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directives it encounters. This is regrettable, but is normally not a
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problem in practice.
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The
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.B moc
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does not handle all of C++. The main problem is that class templates
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cannot have signals or slots. This is an important bug. Here is an
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example:
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.PP
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.in +4
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.nf
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class SomeTemplate<int> : public QFrame {
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TQ_OBJECT
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....
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signals:
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void bugInMocDetected( int );
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};
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.fi
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.in -4
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.PP
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Less importantly, the following constructs are illegal. All of them
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have have alternatives which we think are usually better, so removing
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these limitations is not a high priority for us.
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.SS "Multiple inheritance requires QObject to be first."
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If you are using multiple inheritance,
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.B moc
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assumes that the
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.B first
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inherited class is a subclass of QObject. Also, be sure that
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.B only
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the first inherited class is a QObject.
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.PP
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.in +4
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.nf
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class SomeClass : public QObject, public OtherClass {
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...
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};
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.fi
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.in -4
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.PP
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This bug is almost impossible to fix; since the
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.B moc
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does not expand
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#include or #define, it cannot find out which one of the base classes is a
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QObject.
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.SS "Function pointers cannot be arguments to signals or slots."
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In most cases where you would consider that, we think inheritance is a
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better alternative. Here is an example of illegal syntax:
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.PP
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.in +4
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.nf
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class SomeClass : public QObject {
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TQ_OBJECT
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...
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public slots:
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// illegal
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void apply( void (*apply)(List *, void *), void * );
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};
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.fi
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.in -4
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.PP
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You can work around this restriction like this:
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.PP
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.in +4
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.nf
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typedef void (*ApplyFunctionType)( List *, void * );
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class SomeClass : public QObject {
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TQ_OBJECT
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...
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public slots:
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void apply( ApplyFunctionType, char * );
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};
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.fi
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.in -4
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.PP
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It may sometimes be even better to replace the function pointer with
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inheritance and virtual functions, signals or slots.
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.SS "Friend declarations cannot be placed in signals or slots sections"
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Sometimes it will work, but in general, friend declarations cannot be
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placed in
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.B signals
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or
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.B slots
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sections. Put them in the good old
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.BR private ", " protected
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or
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.B public
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sections instead. Here is an example of the illegal syntax:
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.PP
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.in +4
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.nf
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class SomeClass : public QObject {
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TQ_OBJECT
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...
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signals:
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friend class ClassTemplate<char>; // illegal
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};
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.fi
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.in -4
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.SS "Signals and slots cannot be upgraded"
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The C++ feature of upgrading an inherited member function to
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.B public
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status is not extended to cover signals and slots. Here is an illegal
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example:
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.PP
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.in +4
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.nf
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class Whatever : public QButtonGroup {
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...
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public slots:
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QButtonGroup::buttonPressed; // illegal
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...
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};
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.fi
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.in -4
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.PP
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The QButtonGroup::buttonPressed() slot is protected.
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.PP
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C++ tquiz: What happens if you try to upgrade a protected member
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function which is overloaded?
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.IP
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- All the functions are upgraded.
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.IP
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- That is not legal C++.
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.\" Good idea, but look in the SEE ALSO section...
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.SS "Type macros cannot be used for signal and slot arguments"
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Since the
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.B moc
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does not expand #define, type macros that take an argument
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will not work in signals and slots. Here is an illegal example:
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.PP
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.in +4
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.nf
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#ifdef ultrix
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#define SIGNEDNESS(a) unsigned a
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#else
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#define SIGNEDNESS(a) a
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#endif
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class Whatever : public QObject {
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...
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signals:
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void someSignal( SIGNEDNESS(int) ); // illegal
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};
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.PP
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A #define without arguments works.
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.fi
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.in -4
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.SS "Nested classes cannot be in the signals or slots sections nor have signals or slots"
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Here's an example:
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.PP
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.in +4
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.nf
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class A {
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TQ_OBJECT
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public:
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class B {
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public slots: // illegal
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void b();
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...
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};
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signals:
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class B { // illegal
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void b();
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...
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}:
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};
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.fi
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.in -4
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.PP
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.SS "Constructors cannot be used in signals or slots sections"
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It is a mystery to us why anyone would put a constructor on either the
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.B signals
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or
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.B slots
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sections. You can't, anyway (except that it happens to work in some
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cases). Put them in
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.BR private ", " protected
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or
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.B public
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sections, where they belong. Here is an example of the illegal syntax:
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.PP
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.in +4
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.nf
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class SomeClass : public QObject {
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TQ_OBJECT
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public slots:
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SomeClass( QObject *parent, const char *name )
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: QObject( parent, name ) {} // illegal
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...
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};
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.fi
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.in -4
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.SS "Properties need to be declared before the public section that contains the respective get and set functions"
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.PP
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Declaring the first property within or after the public section that
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contains the type definition and the respective get and set functions
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does not work as expected. The
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.B moc
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will complain that it can neither
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find the functions nor resolve the type. Here is an example of the
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illegal syntax:
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.PP
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.in +4
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.nf
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class SomeClass : public QObject {
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TQ_OBJECT
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public:
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...
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// illegal
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Q_PROPERTY( Priority priority READ priority WRITE setPriority )
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Q_ENUMS( Priority )
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enum Priority { High, Low, VeryHigh, VeryLow };
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void setPriority( Priority );
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Priority priority() const;
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...
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};
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.fi
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.in -4
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.PP
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Work around this limitation by declaring all properties at the
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beginning of the class declaration, right after TQ_OBJECT:
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.PP
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.in +4
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.nf
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class SomeClass : public QObject {
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TQ_OBJECT
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Q_PROPERTY( Priority priority READ priority WRITE setPriority )
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Q_ENUMS( Priority )
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public:
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...
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enum Priority { High, Low, VeryHigh, VeryLow };
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void setPriority( Priority );
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Priority priority() const;
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...
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};
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.fi
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.in -4
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.PP
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.SH "SEE ALSO"
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.BR http://www.trolltech.com ", "
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.BR "C++ ARM, section r.11.3" " (for the answer to the tquiz), and"
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.BR http://doc.trolltech.com " (for complete Qt documentation)."
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