Factorial States Example

The Factorial States example shows how to use The State Machine Framework to calculate the factorial of an integer.

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Publié le 27 décembre 2024 - Mis à jour le 27 décembre 2024

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Factorial States Example▲

The statechart for calculating the factorial looks as follows:

In other words, the state machine calculates the factorial of 6 and prints the result.

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class Factorial : public QObject
{
    Q_OBJECT
    Q_PROPERTY(int x READ x WRITE setX)
    Q_PROPERTY(int fac READ fac WRITE setFac)
public:
    Factorial(QObject *parent = 0)
        : QObject(parent), m_x(-1), m_fac(1)
    {
    }

    int x() const
    {
        return m_x;
    }

    void setX(int x)
    {
        if (x == m_x)
            return;
        m_x = x;
        emit xChanged(x);
    }

    int fac() const
    {
        return m_fac;
    }

    void setFac(int fac)
    {
        m_fac = fac;
    }

Q_SIGNALS:
    void xChanged(int value);

private:
    int m_x;
    int m_fac;
};

The Factorial class is used to hold the data of the computation, x and fac. It also provides a signal that's emitted whenever the value of x changes.

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class FactorialLoopTransition : public QSignalTransition
{
public:
    FactorialLoopTransition(Factorial *fact)
        : QSignalTransition(fact, SIGNAL(xChanged(int))), m_fact(fact)
    {}

    bool eventTest(QEvent *e) override
    {
        if (!QSignalTransition::eventTest(e))
            return false;
        QStateMachine::SignalEvent *se = static_cast&lt;QStateMachine::SignalEvent*&gt;(e);
        return se-&gt;arguments().at(0).toInt() &gt; 1;
    }

    void onTransition(QEvent *e) override
    {
        QStateMachine::SignalEvent *se = static_cast&lt;QStateMachine::SignalEvent*&gt;(e);
        int x = se-&gt;arguments().at(0).toInt();
        int fac = m_fact-&gt;property("fac").toInt();
        m_fact-&gt;setProperty("fac",  x * fac);
        m_fact-&gt;setProperty("x",  x - 1);
    }

private:
    Factorial *m_fact;
};

The FactorialLoopTransition class implements the guard (x > 1) and calculations (fac = x * fac; x = x - 1) of the factorial loop.

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class FactorialDoneTransition : public QSignalTransition
{
public:
    FactorialDoneTransition(Factorial *fact)
        : QSignalTransition(fact, SIGNAL(xChanged(int))), m_fact(fact)
    {}

    bool eventTest(QEvent *e) override
    {
        if (!QSignalTransition::eventTest(e))
            return false;
        QStateMachine::SignalEvent *se = static_cast&lt;QStateMachine::SignalEvent*&gt;(e);
        return se-&gt;arguments().at(0).toInt() &lt;