Qt

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Uses

Binding with different languages

http://qt-project.org/wiki/Category:LanguageBindings

Download of 4.x and 5.x version

http://download.qt-project.org/official_releases/

For example, the source code for 5.0.1 can be downloaded from http://download.qt-project.org/official_releases/qt/5.0/5.0.1/single/

precompiled Qt 4.8.5 MinGW binary

Got an error of 'Only versions with W32API 3.13 are supported'. See https://bugreports.qt-project.org/browse/QTBUG-26137. I am using MinGW-get-setup.exe to install MinGW. The gcc version is 4.7.2-1.

Some suggestions are to install old versions of GCC. http://qt-project.org/forums/viewthread/22352 and http://qt-project.org/wiki/MinGW.

Download gcc 4.4.0 (mingw-gcc440_1.zip) from search google. Just unzip it to C:\. There is no need to put 'C:\mingw\bin' in Windows environment variable PATH. At the end, we will have a new folder C:\mingw.

Although Qt can be installed without any errors, when I try some examples, some of them will give an error "The program has unexpectedly finished". Update: the error was caused by previous build residue. Just delete the build directory (Debug/Release) and re-build again. Things works well. However, remember the executable file can only be run through Qt Creator. It does not work by just double clicking the executable file.

The order of installation is

  1. mingw
  2. Qt library
  3. Qt creator

precompiled Qt 5.1.1 MSVC

I try Qt 5.1.1 for Windows 32bit (VS 2010, OpenGL 504 MB) on my Windows 7 + VS 2010. The <fancybrowser> works fine.

Note that after I install it to "C:\Qt\5.1.1" directory, I will get the following sub-directories "5.1.1" (another one), "Licenses", "Tools", "vcredist" with a few files. The <Qt Creator> cannot be unselect in installation and it is located under "Tools" folder.

Transition of Qt 4.x to 5

http://qt-project.org/wiki/Transition_from_Qt_4.x_to_Qt5

In summary, we need to add the following line to .pro file 

QT += widgets

How to Build static Qt on Windows

General resource:

Why do we need to

Using the VS2010 version of Qt to build an app has a problem when it is time to distribute the application. In my first example of GUI with button & label, I need to put the following 7 dll files in the same exe directory in order to run the exe file from Windows Command Prompt instead of Qt Creator.

  • icudt49.dll (17MB)
  • icuin49.dll (1.3MB)
  • icuuc49.dll (1MB)
  • Qt5Cored.dll (7MB)
  • Qt5Guid.dll (5.5MB)
  • Qt5Widgets.dll (4MB)
  • Qt5Widgetsd.dll (7.5MB)

Google: how to reploy application on windows, how to build qt contains all dll static on windows

My experience based on Qt 4.x.x

MSVC 2010

  • Download and install Perl (no need for python, ruby for Qt 4.8).
  • Unzip source file in zip format and put it under C:\Qt
  • Rename C:\Qt\qt-everywhere-opensource-src-4.8.4 to C:\Qt\4.8.4
  • Open c:\Qt\4.8.4\mkspecs\win32-msvc2010\qmake.conf and replace
QMAKE_CFLAGS_RELEASE = -O2 -MD
QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -O2 -MD -Zi
QMAKE_CFLAGS_DEBUG = -Zi -MDd

with 

QMAKE_CFLAGS_RELEASE = -O2 -MT
QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -O2 -MT -Zi
QMAKE_CFLAGS_DEBUG = -Zi -MTd

according to the page 

cd C:\Qt\4.8.4
set PATH=C:\QT\4.8.4\bin;%PATH%
configure -platform win32-msvc2010 -static -opensource -debug-and-release
nmake sub-src

If we need to reconfigure, run make confclean and configure. Some guide also includes '-release' option.

See here when we want to build both release and debug mode applications. If we just specify '-release' in the configure line, we will not be able to create debug program although I still do not know how to use debug program in Qt creator with MSVC.

For mingw, we need to use 'mingw32-make' instead of 'make' or 'nmake'. See Building Qt Desktop for Windows with MinGW.

MinGW

Download and install MinGW-gcc440_1 & ActivePerl.

C:\Perl64\site\bin, C:\Perl64\bin (these 2 were added by ActivePerl installer by default), C:\mingw\bin and C:\Qt\4.8.5-src should be put in the PATH variable.

I have successfully built Qt using MinGW. 

configure 
mingw32-make

When I try to run my program (either Debug or Release version), I get an error The program can't start because QtCore4.dll is missing from your computer. Try reinstalling the program to fix this problem.. Reboot?

For Qheatmap application, we still need to copy 2 dll files: mingwm10.dll(11 KB) and libgcc_s_dw2-1.dll(43 KB) from C:\mingw\bin folder to the same folder as Qheatmap.exe. These 2 files were also mentioned in Building Qt Desktop for Windows with MinGW.

My experience based on Qt 5.x.x

  • See the instruction on Git
  • The directory structure in Qt 5 is quite different from Qt 4. For example, \bin directory is now under \qtbase directory not under the root directory.
  • read ReadME file to download Perl, Python and Ruby. Make sure the executable path in in PATH env variable.
  • Download/Install Windows SDK 7.1 (for Windows 7) or 8 (for Windows 8).
  • OpenGL (NOT optional): DirectX SDK The 6/7/2010 version is about 572MB. This will be installed to C:\Program Files (x86)\Microsoft DirectX SDK(June 2010) directory. (The precompiled Qt is built against ANGLE which provides OpenGL ES 2.0 support. ANGLE allows Windows users to run OpenGL ES 2.0 content by translating OpenGL ES 2.0 API calls to DirectX 9 API calls) I actually got an error of Error code S1023 when I installed DirectX SDK. See the solution here/Basically uninstall x86 & x64 VC2010 Redistr and install DirectX SDK and then re-install x86 & x64 VC2010 Redistr.
  • modify mkspecs by searching qmake.conf. It was found in C:\Qt\qt-everwhere-opensource-src-5.1.1\qtbase\mkspecs\win32-msvc2010
  • run the following
cd c:\qt\5.1.1-src
set PATH=C:\QT\5.1.1-src\qtbase\bin;C:\qt\5.1.1-src\gnuwin32\bin;%PATH%
set QMAKESPEC=win32-msvc2010

configure -debug-and-release -static -opensource -opengl desktop -nomake examples -nomake tests

jom

It works when I tested qtbase\examples\widgets\painting.

Build Webkit

Try on Qt 5.1.1 

set PATH=%PATH%;C:\icu\bin64
set INCLUDE=%INCLUDE%;C:\icu\include
set LIB=%LIB%;C:\icu\lib64

perl qtwebkit\Tools\Scripts\build-webkit --qt --release --minimal

The WebKit build was disabled for the following reasons:
    * ICU is required. To build QtWebKit with Qt 5 you need to build Qt 5 with l
ibICU support. Check for ICU support being mentioned in qtbase/config.summary.
  • The static build of WebKit is not successful when I use qt source code. I get the message "Project ERROR: WebKit requires SQLite. Either make it available via pkg-config, set $SQLITE3SRCDIR or build Webkit under qt5.git."
# Open Qt command prompt from Windows Start
cd c:\qt\5.1.1\5.1.1\Src\qtwebkit\
perl Tools\Scripts\build-webkit --qt --release --minimal
  • The static build of WebKit is not successful when I use SVN version. I get the message "Failed to set up build environment using SQLite. Either make it available via pkg-config, set $SQLITE3SRCDIR or build WebKit under qt5.git."
  • Another try according to stackoverflow. First of all, we still need to follow the build instruction for QtWebKit build on Windows to install GNU tools and setup PATH. Open a QT command prompt (The Qt was not from source code but from MSVC binary) and
cd C:\qt\5.1.1\5.1.1\src\qtwebkit
qmake

Open another VS 2010 command prompt and 

set PATH=%PATH%;C:\icu\bin64
set INCLUDE=%INCLUDE%;C:\icu\include
set LIB=%LIB%;C:\icu\lib64
SET SQLITE3SRCDIR=C:\qt\5.1.1\5.1.1\src\qtbase\src\3rdparty\sqlite
cd C:\qt\5.1.1\5.1.1\src\qtwebkit
nmake

Still get errors "LNK2001: unresolved external symbol _u_charType_51 JavaScriptCore.lib(Lexer.obj)" as reported by this case. This is a good reference.

Install Qt on Ubuntu

It is also necessary to follow http://qt-project.org/wiki/install_Qt_5_on_Ubuntu to install g++ and OpenGL libraries. Note the last one is what I added to resolve the error of cannot finding -lGL; check Compile Qt 4.7 on Ubuntu 10.10. 

sudo apt-get install build-essential
sudo apt-get install libgl1-mesa-dev

If Qt Creator was installed (eg from binary installer of Qt 5.1.0), then it can be launched by 

~/Qt5.1.0/Tools/QtCreator/bin/qtcreator

Qt 5.x.x

It is straight forward if we use the binary version installer instead of building from Qt source. Just use 'chmod +x' to make the downloaded file executable and then run the executable file. 

./qt-linux-opensource-5.1.1-x86_64-offline.run

It is still necessary to install opengl library by executing sudo apt-get install mesa-common-dev and sudo apt-get install libgl1-mesa-dev.

At the end, the qmake program is available under ~/Qt5.1.1/5.1.1/gcc_64/bin/qmake.

The Qt creator is bundled in the installer so we don't have to download it separately.

Q: How to resolve the error <QPrinter> no such file or directory in Qt 5? Ans: Add QT += printsupport according to http://qt-project.org/forums/viewthread/24668.

Q: How to resolve the error /home/brb/Qt5.1.1/5.1.1/gcc/include/QtCore/qobject.h:214: Error no type named 'Object' in 'struct QtPrivate::FunctionPointer<const char*>'

Qt 4.x.x

Method 1. Use apt-get install approach. See http://www.wikihow.com/Install-Qt-SDK-on-Ubuntu-Linux 

sudo apt-get install qt4-dev-tools

At the time of writing (tested on Linux Mint 15), the qmake is 4.5.2 (the Qt website offers 4.8.5).

Method 2. Manually compile it. First we download Linux/X11 one from qt-project.org (230MB). It is the same as the source code file. The INSTALL file points to http://qt-project.org/doc/qt-4.8/install-x11.html. We also need to do 'apt-get install libxext-dev' to resolve an error that 'basic XLib functionality test failed'. 

tar xzvf qt-everywhere-opensource-src-4.8.5.tar.gz
./configure -static
make
sudo make install

Note that the last step make install is required; if this is skipped, Qt Creator won't let you to add 4.8.5 as a Kit.

At the end of "./configure", it shows 

Qt is now configured for building. Just run 'make'.
Once everything is built, you must run 'make install'.
Qt will be installed into /usr/local/Trolltech/Qt-4.8.5

To reconfigure, run 'make confclean' and 'configure'.

In .profile (if your shell is bash, ksh, zsh or sh), add the following lines: 

 PATH=/usr/local/Trolltech/Qt-4.8.5/bin:$PATH
 export PATH

Qt Creator

  • Multiple version of Qt library
  • Keyboard shortcuts:
    • Ctrl + Click the symbol - move to the definition or the declaration of a symbol.
    • Click a symbol + Right click + Follow the symbol under cursor - move to the definition
  • The default build directory is parallel to the folder of source code which is a pain if there is a same project name. A better default build directory should be under the source code folder. To change the default setting, go to Tools -> Options -> Build and Run -> Remove "../" from the Default build directory value "../build-%{CurrentProject:Name}-%{CurrentKit:FileSystemName}-%{CurrentBuild:Name}". The project name is determined by Qt project file XXXX.pro.
  • here teaches us how to set warning level when compiling a Qt project. Qt project uses the settting in makefile. We can overwrite it by setting something in .pro file
win32:QMAKE_CXX_FLAGS_WARN_ON += -Wextra

Google: Qt change warning level.

Qt Tutorial

Qt forum

http://www.qtcentre.org/forum

Simple Test

To quickly test whether the Qt was built successfully, we can 

cd c:\Qt
mkdir example
cd example
notepad test.cpp
set PATH=%PATH%;C:\QT\4.8.4\bin
qmake -project
qmake
nmake

If everything went well, we will obtain the executable file under release folder. That is, we can run the executable file by 

release\example.exe

Qt-Apps.org

http://qt-apps.org/ is a good source to find open source projects based on Qt.

Graphics

Scientific

Qt Widget

Qt games

C++ basics

See C++ tutorial.

  • Use dot (.) to refer to any public member of a class.
  • Use the arrow operator (->) to refer to a member of an object pointed by a pointer. The label below is a pointer rather than an object but *label is an object.
QLabel *label = new QLabel("ABCDE");
label->show();
// (*label).show();
  • Use the operator of scope (::) to set a definition of a class's member function or call a function from some class. For example,
QObject::connect();

means to use connect() function from QObject class.

  • The this pointer passed on to the EditDialog sets the parent of the dlg to the list dialog.
EditDialog dlg( this );

Here explains: The keyword this identifies a special type of pointer. Suppose that you create an object named x of class A, and class A has a nonstatic member function f(). If you call the function x.f(), the keyword this in the body of f() stores the address of x..

Qt Basic

Q_OBJECT

This macro is required if a class contains SIGNAL/SLOT.

tr()

tr() means translation; the characters were auto translated depending on system's locale. See http://qt-project.org/doc/qt-4.8/linguist-hellotr.html

Run Qt from Command Line

I use 

# Open command prompt from Visual Studio 2010
set PATH=C:\Qt\Qt5.0.2\5.0.2\msvc2010_opengl\bin;%PATH%

Now we can build the project by for example 

cd C:\Qt\FQD\Chapter01\plain-cpp
qmake -project
qmake
nmake

The executable will be located under release subfolder.

From C++ to Qt

See Chap 1 of Foundation of Qt Development book.

No Qt Qt
Class List 1.1 
#include <string>
using std::string;
class MyClass
{
public:
  MyClass (const string & text);
  const string& text() const;
  void setText (const string& text);
  int getLengthOfText() const;
private:
  string m_text
}
List 1.2 
#include <QObject>
#include <string>
using std::string;
class MyClass : public QObject
{
public:
  MyClass (const string& text, QObject *parent = 0);
...
}
Main List 1.3 
#include <iostream>
int main(int argc, char **argv)
{
  MyClass *a, *b, *c;
  a = new MyClass ("foo");
  b = new MyClass("ba-a-ar");
  c = new MyClass("baz");
  std::cout << a->text() << "(" << a->getLengthOfText() << ")" << std::endl;
  a->setText( b-> text() );
  std::cout << a->text()  << "(" << a->getLengthOfText() << ")" << std::endl;
  int result = a->getLengthOfText() - c ->getLengthOfText();
  delete a;
  delete b;
  delete c;
  return result;
}
List 1.4 
#include <QtDebug>
int main (int argc, char **argv)
{
  QObject parent;
  MyClass *a, *b, *c;
  a = new MyClass ("foo", &parent);
  b = new MyClass("ba-a-ar", &parent);
  c = new MyClass ("baz", &parent);
  qDebug() << QString::fromStdString(a->text()) << "(" << a->getLengthOfText() << ")";
  a -> setText( b-> text());
  qDebug() << QString::fromStdString(a->text()) << "(" << a->getLengthOfText() << ")";
  return a->getLengthOfText() - c->getLengthOfText();
}

Naming Convention

  • Class name starts with an uppercase letter and the words are divided using Camel-Casing.
  • The names of the methods all start with a lowercase letter, and the words are again divided by using CamelCasing.

Memory Management

Parent is on heap. So it has to be deleted manually. 

#include <QtGui>
#include "addressbook.h"
//...every needed header

int main(...) {
   //QApplication app ....
   QWidget *parent = new QWidget; //a parent for your addressbook 
   AddressBook *myAddressBook = new AddressBook(parent); //pass a pointer to parent widget when you construct an AddressBook object
   //... other code, maybe some layout if necessary...
   parent->show(); //will show the chidren widgets too
   
   int returnValue = app.exec();
   delete parent; //this will delete the parent children too
   return returnValue;
}

OR creating parent on the stack 

int main(...) {
   //QApplication app ....
   QWidget parent; //a parent for your addressbook - parent is created on stack
   AddressBook *myAddressBook = new AddressBook(&parent); //pass a pointer to parent widget when you construct an AddressBook object
   //... other code, maybe some layout if necessary...
   parent.show(); //will show the chidren widgets too

   return app.exec();
}

Misc

  • If we want to create a new class member to be used in class method, we should declare it in the header file. For example, look at the variable 'label' below. Of course, variables only used locally have not this rule.
class MyButton : public QWidget
{
   Q_OBJECT
public:
    MyButton(QWidget *parent = 0);
    QLabel *label;
private slots:
    void showText();
};

MyButton::MyButton(QWidget *parent)
    : QWidget(parent)
{
  label = new QLabel(); // NOT QLabel *label = new QLabel();
}

void MyButton::showText()
{
  label->setText("My Text!");
}

Qt Quick

Qt Tricks

Set Windows initial posiiton

Set main window initial position

Qt5 is complaining 'QApplication: No such file or directory ...'

The solution is to add 

QT += widgets

to your .pro file.

Get the current working path

Use QCoreApplication::applicationDirPath() to get the current working path or QFile::absolutePath() to get the absolute path from relative one.

Pop up a help file

  • QMessageBox: no maximize button on top-right corner. Cannot resize (old Qheatmap)
  • QTextBrowser: the html file cannot be part of C++ (Qtextbrowser)
  • QLabel: No scroll bar (Qt07_BasicApplication)
  • QTextEdit: Good (used in Qheatmap)
  • QWebkit
  • QTextDocument: no scroll bar (Qt79_drawText)

Convert QString to std::string

http://stackoverflow.com/questions/4214369/how-to-convert-qstring-to-stdstring 

.toStdString()

Custom Plots

Use boost libraries with an example

http://stackoverflow.com/questions/16998326/using-boost-libraries-in-qt

On Windows OS, we can add the following to the .pro file 

INCLUDEPATH += C:/boost/boost_1_53_0/
LIBS += "-LC:/boost/boost_1_53_0/stage/lib/"

On Ubuntu OS, I can use (the first line Qt += widgets is only necessary on Qt 5) 

QT += widgets
INCLUDEPATH += /home/brb/Downloads/boost_1_55_0/
LIBS += "-L/home/brb/Downloads/boost_1_55_0/stage/lib/"

The following is an example to compute the 95% percentile from the T distribution (df=195) is 

#include <QApplication>
#include <QLabel>

#include <boost/math/distributions/students_t.hpp>

using namespace std;
using boost::math::students_t;

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    int df = 195;
    double alpha = .1;
    students_t dist(df);
    double T = quantile(complement(dist, alpha / 2));

    QLabel *label = new QLabel("T(.95, df=195)=" + QString::number(T));
    label->show();

    return a.exec();
}

Home directory

QDir::homePath()

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