random technical notes

class MainWindow : public QMainWindow
{
 Q_OBJECT;
public:
 MainWindow(QWidget *parent = 0) : QMainWindow(parent)
 {
   QSettings settings;
   restoreGeometry(settings.value("mainWindowGeometry").toByteArray());
   // create docs, toolbars, etc...
   restoreState(settings.value("mainWindowState").toByteArray());
 }

 void closeEvent(QCloseEvent *event)
 {
   QSettings settings;
   settings.setValue("mainWindowGeometry", saveGeometry());
   settings.setValue("mainWindowState", saveState());
 }
};

int main(int argc, char *argv[])
{
 QApplication a(argc, argv);
 QCoreApplication::setOrganizationDomain("OrgDomain");
 QCoreApplication::setOrganizationName("OrgName");
 QCoreApplication::setApplicationName("AppName");
 QCoreApplication::setApplicationVersion("1.0.0");

 MainWindow w;
 w.show();

 return a.exec();
}

The above code will save and restore window position, size, toolbar visibility, toolbar docking area, dock states, locations and sizes. It saves using QSettings which will store your settings in a platform correct way.

Source

Get 97 short and extremely useful tips from some of the most experienced and respected practitioners in the industry, including Uncle Bob Martin, Scott Meyers, Dan North, Linda Rising, Udi Dahan, Neal Ford, and many more. They encourage you to stretch yourself by learning new languages, looking at problems in new ways, following specific practices, taking responsibility for your work, and becoming as good at the entire craft of programming as you possibly can.

O’Relly homepage

There is the 97 Things Every Programmer Should Know project, pearls of wisdom for programmers collected from leading practitioners. You can read through the Contributions Appearing in the Book.

Russian translation of these tips.

In information theory and computer science, the Levenshtein distance is a metric for measuring the amount of difference between two sequences (i.e. an edit distance). The term edit distance is often used to refer specifically to Levenshtein distance.

The Levenshtein distance between two strings is defined as the minimum number of edits needed to transform one string into the other, with the allowable edit operations being insertion, deletion, or substitution of a single character. It is named after Vladimir Levenshtein, who considered this distance in 1965. (wikipedia with code, russian version)

• Levenshtein Distance, in Three Flavors (java applet)
• Damerau–Levenshtein distance
• Levenstein distance.beam (slideshare presentation)

QLatin1String : Avoid mallocs in operator ”==”

if (fruit== "apple") { ... } // hidden malloc

if (fruit== QLatin1String("apple")) { ... } // fast and mentions encoding

QStringRef : String manipulation without the malloc

QString::reserve and QString::squeeze

QStringBuilder : Fast QString concatenation

if (foo.startsWith("(" + type + ") 0x"))

if (foo.startsWith("(" % type % ") 0x"))

Use QStringMatcher to match a string repetitively

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.

Homepage

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.

Documentation

• Classes:
  • QtSingleApplication
  • QtSingleCoreApplication
• Examples
  • A Trivial Example
  • Loading Documents
  • A Non-GUI Example

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

// they both get their own thread
QThread producerThread;
producer.moveToThread(&producerThread);

QThread consumerThread;
consumer.moveToThread(&consumerThread);

// go!
producerThread.start();
consumerThread.start();

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

#include <vector>
#include <string>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <iterator>

int main(int argc, char* argv[])
{
    std::vector<std::string> v;
    std::ifstream f("e:/test.txt");
    if(f.is_open())
    {
        std::copy(std::istream_iterator<std::string>(f),
                  std::istream_iterator<std::string>(),
                  std::back_inserter(v));
    }
    // проверка
    std::copy(v.begin(), v.end(),
              std::ostream_iterator<std::string>(std::cout, "\n"));

    return 0;
}

rsdn.ru

#define YEAR ((((__DATE__ [7] - '0') * 10 + (__DATE__ [8] - '0')) * 10 \
              + (__DATE__ [9] - '0')) * 10 + (__DATE__ [10] - '0'))

#define MONTH (__DATE__ [2] == 'n' ? 0 \
               : __DATE__ [2] == 'b' ? 1 \
               : __DATE__ [2] == 'r' ? (__DATE__ [0] == 'M' ? 2 : 3) \
               : __DATE__ [2] == 'y' ? 4 \
               : __DATE__ [2] == 'n' ? 5 \
               : __DATE__ [2] == 'l' ? 6 \
               : __DATE__ [2] == 'g' ? 7 \
               : __DATE__ [2] == 'p' ? 8 \
               : __DATE__ [2] == 't' ? 9 \
               : __DATE__ [2] == 'v' ? 10 : 11)

#define DAY ((__DATE__ [4] == ' ' ? 0 : __DATE__ [4] - '0') * 10 + (__DATE__ [5] - '0'))

#define DATE_AS_INT (((YEAR - 2000) * 12 + MONTH) * 31 + DAY)

int main (void)
{
  printf ("%d-%02d-%02d = %d\n", YEAR, MONTH + 1, DAY, DATE_AS_INT);
  return 0;
}

static LPTOP_LEVEL_EXCEPTION_FILTER m_previousFilter = NULL;


typedef BOOL (WINAPI *MINIDUMPWRITEDUMP)(HANDLE hProcess, DWORD dwPid, HANDLE hFile, MINIDUMP_TYPE DumpType,
                                         CONST PMINIDUMP_EXCEPTION_INFORMATION ExceptionParam,
                                         CONST PMINIDUMP_USER_STREAM_INFORMATION UserStreamParam,
                                         CONST PMINIDUMP_CALLBACK_INFORMATION CallbackParam);

static LONG WINAPI MyUnhandledExceptionFilter(PEXCEPTION_POINTERS pExceptionInfo)
{
    HMODULE hDll = ::LoadLibrary(_T("DBGHELP.DLL"));
    MINIDUMPWRITEDUMP pDump = (MINIDUMPWRITEDUMP)::GetProcAddress(hDll, "MiniDumpWriteDump");

    _MINIDUMP_EXCEPTION_INFORMATION ExInfo;
    ExInfo.ThreadId = ::GetCurrentThreadId();
    ExInfo.ExceptionPointers = pExceptionInfo;
    ExInfo.ClientPointers = NULL;

    MINIDUMP_CALLBACK_INFORMATION mci;

    // HANDLE hFile - minidamp file name(for example, "test.dmp")

    BOOL bOK = pDump(::GetCurrentProcess(), ::GetCurrentProcessId(),
                     hFile, 1, &ExInfo, NULL, &mci);
}


void main()
{
    // setup our own ExceptionHandler
    m_previousFilter = SetUnhandledExceptionFilter(MyUnhandledExceptionFilter);

    // actial work

    // befoe exit
    if (m_previousFilter)
    {
        SetUnhandledExceptionFilter(m_previousFilter);
    }
}