BCD Adder (Binary-coded decimal)

Binary Code Decimal (BCD) Adder.

This is a tool that helps you add two decimals as BCD.

Why is BCD adder useful?

Double and Float sometimes do not meet the requirement of precision. For example, you cannot hold more than 17 digits in double.

With this BCD adder, you can add numbers with 10^18 digits!



Source: https://github.com/crystalcoding/HappyHacking/tree/master/BCD/bcd_gui


Download (windows binary): http://dl.dropbox.com/u/58798915/release-BCD-v0.9.zip

Qt Djvu, Short Template to Extract Target Line in Current Directory

It's a boilerplate for reading and parsing files.

Just throw in your "process" interface that can do

all the heavy duty work.

The code can:
1. read all files in the current directory
2. extract all lines which contain http://


http://code.google.com/p/mixtools/source/browse/trunk/qt/extract_url_in_files.cpp

Qt, Knuth' Shuffle

http://code.google.com/p/mixtools/source/browse/trunk/qt/card_shuffle/widget.cpp

Qt, Understand The UI Designer

QtCreator uses a very cleaver way to separate the GUI part of your widget through
1. Composition
2. Namespace
(This two steps avoid the inheritance)

In essence,
1. The generated UI class can help generate all GUI-widgets for you (button, textline)
2. The generated UI class has a setupUi method (taking your non-gui widget as an argument),
and the method will use your non-gui widget as the single parent of all the auto-generated widgets. (very cleaver!)
3. In your non-gui widget constructor,
a. you generate a new UI class
b. call setupUi
4. but now, how do you refer to the auto-generated widgets created in the Ui class?
No problem! remember the Ui class is also a "member" of your non-gui widget.
5. So you can call connect, layout etc. to interact with your Ui class.
6. In the destructor of your non-gui widget, it can free the memory (delete ui) when your non-gui widget is dead or out of scope.

Qt, Qt's Build System

qmake -- creates platform specific make file for your platform. Then you can run your native compiler later with your generated make file. Make sure you have a .pro (Qt's project file). It is a configuration file for qmake. E.g. telling the name of the your source file, what Qt module you need (QtNetwork, QtGui, etc...).

moc -- meta object compiler convert signal/slot into standard C++ file.
uic -- creates header files for .ui designer file
rcc -- process the .qrc resource file

Qt, Install Qt Creator in FreeBSD

Qt Creator, a great Qt IDE for C/C++ programming, is officially supported by FreeBSD! This is such a wonderful news! We can compile and install Qt Creator simply using the port collection. (Aug 19, 2009)

Just do:
cd /usr/ports/devel/qtcreator/ && make install clean

Make sure you install the right gdb, if your default gdb (/usr/bin/gdb) does not work with QtCreator. And tell Qt Creator to use the right debugger (e.g. /usr/local/bin/gdb66)

cd /usr/ports/devel/gdb6/ && make install clean

Qt LGPL with Closed Source Software

Using Qt enables the software to be closed source when you "redistribute" it. (It is an important concept. E.g., Google uses GPL Linux kernel "internally" to avoid licensing issue")

So, with Qt's LGPL:

• Dynamically link the Qt library, with your source code closed.
• The installer can download the Qt library if needed.
  
• If you modify the Qt library, you must open up the change.
  

Note:

• You might need to provide your object file. (so people can re-link with the Qt's library)
  
• Ask a lawyer if you are in a serious business, or the licensing violation can be very expensive.
  

Qt Creator Missing lfreetype

Qt cannot compile project under Ubuntu (Linux) because of the error
/usr/bin/ld: cannot find -lfreetype

So the library freetype is missing. Qt Creator requires the development package of fonts. Try install them. In Ubuntu, for example,

apt-get install libglib2.0-dev libSM-dev libxrender-dev libfontconfig-dev libxext-dev

Qt qobject_cast advantage

qobject_cast is like dynamic_cast; it can cast object inherits from QObject.
The advantage is qobject_cast does not require RTTI support

To use it, make sure Q_OBJECT macro is included. Or the return type is undefined.

StackedWidget *stackedWidget = qobject_cast(parent());
if(stackedWidget != 0)
//do something

Qt Shopping List with ListWidget

• Print PDF with QPainter::drawText. Remember to set the coordinate correctly.
  
• Remeber to set the margin for the gridLayout

Source: http://code.google.com/p/mixtools/source/browse/#svn/trunk/qt/listWidget

Qt Debuging Tips

Output:

• qDebug() : e.g. qDebug() << "Stuff:" <<>
• qCritical(): e.g. qCritical("no more memory");
• qFatal();
• qWarning()

Assertion:

• Q_ASSERT()
• Q_ASSERT_X(): this can print the line where assertion fail

Check pointer:

• Q_CHECK_PTR()

Run qmake again:

• error like "vtbl, _vtbl": this might be related to meta-object compiler, check if using Q_OBJECT correctly, make sure the signal/slot syntax (declaration/implementation), and re-run qmake.

Also read the Qt 4.5 Debug Documentation.

Qt S60 Video

Lessons learn from this video:

• In QDesigner, select all widget and group them with layout.
• listWidget is handy.
• window.showMaximized()
• he types very fast and no error

Original Post:
http://labs.trolltech.com/blogs/2009/06/25/the-new-pre-release-of-qt-for-s60-is-there/

Qt Remove * from a string

1. remove string
2. auto copy to clipboard

QTextCodec::setCodecForLocale(QTextCodec::codecForName("Big5"));

QClipboard *clipboard = QApplication::clipboard();

QString input = clipboard->text();

ui->inputBrowser->setPlainText(input);

QString output = "";

foreach(QChar c, input)

{

if ( c != '*') output += c;

}

ui->outputBrowser->setPlainText(output);

clipboard->setText(output);

source: http://code.google.com/p/mixtools/source/browse/#svn/trunk/qt/kill_stars

Qt Tutorial Notes

source : http://code.google.com/p/mixtools/source/browse/#svn/trunk/qt/tutorial/tutorial
http://doc.trolltech.com/4.3/tutorial.html

T4:

• qApp is a global variable
• Put widget on heap, so Qt can manage the memory for you

T5:

• treat layout as the parent of widgets being enclosed
• How to overflow?

T6:

• Remember to show() the widget
• setLayout() takes a "pointer" as the argument
• qRand() returns a value between 0 and RAND_MAX (defined in and )
• check out more global variable in Qt: http://doc.trolltech.com/4.2/qtglobal.html
  

T7:

• Signal can connect to signal: so you fire another signal.
• Two ways to fire a signal: 1. signal connect to signal 2. directly fire it with emit
  
• Cannot treat signal as slot
• Signal is automatically generated by MOC (meta-object compiler), so do not implement it yourself, or you will get duplicate definition.
  
• The Q_OBJECT macro must be used in all subclass of QObject, or the signal/slot will not work. Put the Q_OBJECT in the header file, and put the .h file in .pro file. This way qmake can search source and header files for the Q_Object macro. It will generate build instruction for moc.
• slots can be public, protected, and private
• To declare signal, just do "signals:"
  

T8:

• setFocus()
• setFocusProxy()
• QString::Number() convert number to string
• use "&" to set the button shortcut with Alt

T9:

• Understand The Coordinate System of Qt
• QRect: upper-left + width + height
• drawPie: 0 is 3 o'clock, and draws counter-clockwise
• QPainter::rotate(): on coordinate, and counter-clockwise
• QTimer::start(int millisecs interval), stop(), isActive()

• QTimer::singleShot(600000, &app, SLOT(quit()));
  

T11:

• Understand save() and restore()
  

Qt Auto Resize with Qt Designer

If the Qt designer does not seem to handle the resizing of your widgets when running the application, check the following:

1. To make a widget auto-sizable by itself, it needs to be placed in the layout.
2. Call the setLayout(top_most_layout_from_the_designer) at the place where you use the designer's code (the place where you call setupUi())
   e.g. ui->setupUi(this);
   setLayout(ui->verticalLayout_2);

*because a Layout object is a container for other widgets,
we re-set the layout using ui's layout.

Now the widgets inside the layout can be auto-resize in the Qt Designer.

Convince yourself that all the GUI work should be taken care of by the Designer, if you are using it. Try not to alter the code generated by the Qt Designer (the ui header file). The generated file will be overwritten next time you make change, and that's inconvenient. Unless you really want to handle the resizing yourself, do not implement the resizeEvent. Your code might break i n the future on different machine with different resolution.

Qt Transparent Background on Widget

It is very easy to make the Qt's widget transparent.
source code : https://github.com/crystalcoding/HappyHacking/tree/master/qt/mama-win

this->setWindowOpacity(0.5); //Make the widget half-transparent

For X11, Qt needs a composition manager. For Windows, it will just work.

This method is available for widget or subclass of widget. Under  module QtGui

Qt deployment with Qt Creator

The installation or deployment of Qt Application with shared library, it just needs to:

1. Copy the .exe file
2. And put the required .dll file in the same directory of your .exe file (e.g. QtCore.dll, QtNetwork.dll)
   

Some problems (Under Windows):

The procedure entry point _Z21qRegisterResourceDataiPKhS0_S0 could not be located in the dynamic link library QtCore4.dll

The weird thing is that QtCore4.dll is in the same directory of the .exe file. So what is the error? Just as it said, the QtCore4.dll does not contain the symbol!
Solution: make sure to copy the right QtCore4.dll

1. Search the Qt SDK install directory, find the RIGHT QtCore4.dll
2. In this specific example, do not get the QtCore4.dll under C:\Qt\2009.02\bin,
   but in the Qt directory. E.g. C:\Qt\2009.02\qt\bin
3. Find the QtCore4.dll and QtGui4.dll there, and mingwm10.dll might be needed there if this is a LGPL version.

If you are using Linux/UNIX:
Try ldd command, this cool program list all the dependencies for your executable
For example, ldd your_program_ , it might output
libQtCore.so.4 => /usr/local/lib/qt4/libQtCore.so.4 (0x800648000)
libz.so.5 => /lib/libz.so.5 (0x80099e000)
libgthread-2.0.so.0 => /usr/local/lib/libgthread-2.0.so.0 (0x800ab2000)
libglib-2.0.so.0 => /usr/local/lib/libglib-2.0.so.0 (0x800bb6000)
libiconv.so.3 => /usr/local/lib/libiconv.so.3 (0x800d71000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x800f6b000)
libm.so.5 => /lib/libm.so.5 (0x801176000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x801296000)
libthr.so.3 => /lib/libthr.so.3 (0x8013a4000)
libc.so.7 => /lib/libc.so.7 (0x8014bc000)
libz.so.4 => /lib/libz.so.4 (0x8016f5000)
libintl.so.8 => /usr/local/lib/libintl.so.8 (0x801809000)
libpcre.so.0 => /usr/local/lib/libpcre.so.0 (0x801912000)

Qt Internationalization

1. Add translation file to myapp.pro file.
   e.g. TRANSLATION = app_de.ts
2. Run lupdate on the .pro file (in cmd prompt/console) to generate translation sources in XML-based format. lupdate will generate the .ts file for you.
   e.g. lupdate myapp.pro
3. Run Linquist to load the .ts file.
   Put translation strings of your choices there, and then Ctrl+Enter to accept each string.
4. Generate the binary translation file (.qm), so that you can load it at run time.
   lrelease myapp.pro
5. In your code, create a QTranslator object, QTranslator.load(your .qm file), and then QApplication.installTranslator(your QTranslator object)

Qt Mama Assistant

A program that can easily launch browser to talk to the Internet.

Source Code:
http://code.google.com/p/mixtools/source/browse/#svn/trunk/qt/mama