Some questions in Qt's Source Code

[vql]

I want to develop some widgets for my project, I read Qt's widget source code & have some questions in programming:

1. The constructor of QAbstractButton:

explicit QAbstractButton (QWidget *parent = 0)

explicit QAbstractButton (QWidget *parent = 0)

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What is the purpose and the meaning to using the keyword explicit in constructor?

2. In the function QToolButtonPrivate:opupTimerDone(), some commands I don't understand:

QPointer<QMenu> actualMenu; //the type of actualMenu is'n a pointer
...
if (...)
    actualMenu = menuAction->menu();
else
    actualMenu = new QMenu(q); //but in this code, it used as a pointer

QPointer<QMenu> actualMenu; //the type of actualMenu is'n a pointer
...
if (...)
    actualMenu = menuAction->menu();
else
    actualMenu = new QMenu(q); //but in this code, it used as a pointer

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3. The relationship between QToolButton & QToolButtonPrivate (similar for other classes).

4. Using macro:

#define QTTR_NOOP(x) [B](x)[/B] // this macro has the result
#define Q_DOC_PROPERTY(text) // but this macro doesn't have the result

#define QTTR_NOOP(x) [B](x)[/B] // this macro has the result
#define Q_DOC_PROPERTY(text) // but this macro doesn't have the result

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#define Q_D(Class) Class##Private *const d=d_func()
#define Q_Q(Class) Class *const q=q_func()

#define Q_D(Class) Class##Private *const d=d_func()
#define Q_Q(Class) Class *const q=q_func()

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I don't understand the declare of these macros. Please explain it.


Thanks alot.