Posts Tagged ‘Qt’

Generate a Visual Studio 2010 project file from a qmake pro file

January 10th, 2011 No comments

qmake -spec win32-msvc2010 -tp vc <project_file>.pro

Qt Developer Days 2010

December 30th, 2010 No comments

Videos from Keynotes, Technical Talks, Qt in Education, Qt in Use and Qt Training

This year’s conference program offered three full days of training, technical sessions and Qt in Use presentations. Whether you are a new Qt user, a Qt pro, CTO or Product Manager, Qt Developer Days features more than 50 technical sessions, demos, hands-on labs, compelling case studies and information on partner services to satisfy all your Qt requirements.

Qt Quick for C++ Developers. For those experienced in Qt and C++, but new to QML.

This presentation will focus on those who already know Qt but want to see what QML changes for them. We will show how Qt developers can use the new C++ APIs to register new types and objects. We will also present guidelines to create hybrid C++/QML applications.

Using QString effectively

October 12th, 2010 No comments

Qt State Machine Code Generator

August 19th, 2010 No comments

This add-in for StarUML exports modeled state machine(s) to Qt C++ code.

The add-in can speed up developing state machines when you need to only model a state machine with StarUML and then export it to source code, instead of maintaining the model and code separately.

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Using QString effectively

June 22nd, 2010 No comments

QLatin1String : Avoid mallocs in operator ”==”

Creating a QString from a C-string involves a malloc. For example, there is a hidden-malloc cost in the following code.
if (fruit== "apple") { ... } // hidden malloc
In the code above, “apple” gets converted into a QString using QString::fromAscii(). This means that QString will allocate memory for the string “apple” and creates a deep copy of the C-style string. This deep copy is not really necessary and can be avoided by not creating a QString to start with and if the encoding of the C-string was somehow known. Since Latin-1 string comparisons are most common, Qt provides a special class called QLatin1String that just holds a pointer to the C-string provided in it’s constructor. In addition, QString provides a QString::operator==(const QLatin1String &) overload that has special code to compare without malloc+deep copy. We can make the above code fast by writing it instead as,
if (fruit== QLatin1String("apple")) { ... } // fast and mentions encoding

QStringRef : String manipulation without the malloc

QString has various methods for string manipulations like mid(), left(), right(). All of them create a new QString and hence a malloc/deep copy of data in an existing QString. Instead, one can use QString::midRef(), QString::leftRef() and QString::rightRef() to obtain a QStringRef. A QStringRef is a reference of a portion of a QString. QString also provides many overloads like QString::operator==(const QStringRef &) for optimizations with QStringRef.

QString::reserve and QString::squeeze

If you expect a QString to grow, it’s better to call QString::reserve to allocate extra memory in advance so that every call to QString::append() does not result in a malloc. Extra memory can be reclaimed using QString::squeeze.

QStringBuilder : Fast QString concatenation

The code below requires atleast 2 mallocs.
if (foo.startsWith("(" + type + ") 0x"))
Qt 4.6 introduces an internal class called QStringBuilder that “reserves” memory for a concatenation chain in a single shot. It does so by having each of the + operations above return a different class (not QString). This class keeps track of the string’s that are being appended and the required memory at each step. At the final step, where the concatenation operation gets converted into a QString it allocates memory in a single shot and copies all the strings in the chain one after another. This features can be enabled by using QT_USE_FAST_CONCATENATION. With this defined, one can use the operator ’%’ instead of ’+’. One would now write,
if (foo.startsWith("(" % type % ") 0x"))
If we want to use ’+’ itself instead of ’%’, one can also define QT_USE_FAST_OPERATOR_PLUS. See Fast concatenation for more details

Use QStringMatcher to match a string repetitively

If you are looking for a string repetitively in many strings or in the same string many times, you should use QStringMatcher. It uses Boyer-Moore string search algorithm to perform fast searches.


June 22nd, 2010 No comments

The QtService component is useful for developing Windows services and Unix daemons.

The project provides a QtService template class that can be used to implement service applications, and a QtServiceController class to control a service.

On Windows systems the implementation uses the Service Control Manager.

On Unix systems services are implemented as daemons.


Single Application

June 19th, 2010 No comments

The QtSingleApplication component provides support for applications that can be only started once per user.

For some applications it is useful or even critical that they are started only once by any user. Future attempts to start the application should activate any already running instance, and possibly perform requested actions, e.g. loading a file, in that instance.

The QtSingleApplication class provides an interface to detect a running instance, and to send command strings to that instance.

For console (non-GUI) applications, the QtSingleCoreApplication variant is provided, which avoids dependency on QtGui.


Download Open Source Edition (LGPL):


June 18th, 2010 No comments

QThread was designed and is intended to be used as an interface or a control point to an operating system thread, not as a place to put code that you want to run in a thread. We object-oriented programmers subclass because we want to extend or specialize the base class functionality. The only valid reasons I can think of for subclassing QThread is to add functionality that QThread doesn’t have, e.g. perhaps providing a pointer to memory to use as the thread’s stack, or possibly adding real-time interfaces/support. Code to download a file, or to query a database, or to do any other kind of processing should not be added to a subclass of QThread; it should be encapsulated in an object of it’s own.

You’re doing it wrong…

// create the producer and consumer and plug them together
Producer producer;
Consumer consumer;

bool bOk = producer.connect(&consumer,
bOk = consumer.connect(&producer,
                       SIGNAL(produced(QByteArray *)),
                       SLOT(consume(QByteArray *)));

// they both get their own thread
QThread producerThread;

QThread consumerThread;

// go!

Reference: Threading without the headache or QThread’s no longer abstract (see attached file)

MeeGo Netbook Release

May 27th, 2010 No comments

The following MeeGo v1.0 images are available for download:

Installing MeeGo on your Netbook

MeeGo 1.0

MeeGo v1.0 Core Software Platform & Netbook User Experience project release

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MinGW and Qt Creator: Interrupt/Exception caught code = 0xc00000fd

March 7th, 2010 No comments

On Windows Vista 64-bit or Windows 7 64-bit, GCC make (MinGW) can be failed with the error:

mingw32-make.exe: Interrupt/Exception caught (code = 0xc00000fd, addr = 0x421963)

Read more…

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