QT_BEGIN_NAMESPACE question

[veraS]

Hi,
What is the diference in using ...

QT_BEGIN_NAMESPACE
class QLabel;
class QPushButton;
class QUdpSocket;
QT_END_NAMESPACE

QT_BEGIN_NAMESPACE
class QLabel;
class QPushButton;
class QUdpSocket;
QT_END_NAMESPACE

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or

#include <QLabel>
#include <QPushButton>
#include <QUdpSocket>

#include <QLabel>
#include <QPushButton>
#include <QUdpSocket>

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... in my dialogs?
Thanks

[SixDegrees]

The first method can be faster; the compiler doesn't need to process the contents of the header files as it does in the second method. This only affects compilation time, and on the systems I've used there is no perceptible difference in compilation speed. On large projects, or where you have a large number of include files, it may make more of a difference.

[veraS]

In the broadcastreceiver example i have:

#ifndef RECEIVER_H
#define RECEIVER_H
 
#include <QDialog>
 
QT_BEGIN_NAMESPACE
class QLabel;
class QPushButton;
class QUdpSocket;
QT_END_NAMESPACE
 
class Receiver : public QDialog
{
    Q_OBJECT
 
public:
    Receiver(QWidget *parent = 0);
 
private slots:
    void processPendingDatagrams();
 
private:
    QLabel *statusLabel;
    QPushButton *quitButton;
    QUdpSocket *udpSocket;
};
 
#endif

#ifndef RECEIVER_H
#define RECEIVER_H

#include <QDialog>

QT_BEGIN_NAMESPACE
class QLabel;
class QPushButton;
class QUdpSocket;
QT_END_NAMESPACE

class Receiver : public QDialog
{
    Q_OBJECT

public:
    Receiver(QWidget *parent = 0);

private slots:
    void processPendingDatagrams();

private:
    QLabel *statusLabel;
    QPushButton *quitButton;
    QUdpSocket *udpSocket;
};

#endif

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Why use #include for the QDialog class and QT_BEGIN_NAMESPACE...QT_END_NAMESPACE for QLabel, QPushButton and QUdpSocket?

[SixDegrees]

Because Receiver inherits from QDialog; the compiler needs the actual class definition provided in the header file in order to resolve the internal structure of the class. The other classes are only referenced through pointers, so a simple forward declaration is sufficient for the compiler in those cases.