Forward declarations needed for some?

[doktorn]

Hello.

This is a question to still my curiosity about forward declarations. According to Blanchette and Summerfield's book, forward declarations is needed only to make compilation "somewhat faster". But I just got problems for not having them onboard in my program.

incomehandler.h:21: error: ISO C++ forbids declaration of `QLabel' with no type
incomehandler.h:21: error: expected `;' before '*' token

incomehandler.h:21: error: ISO C++ forbids declaration of `QLabel' with no type
incomehandler.h:21: error: expected `;' before '*' token

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I commented after the declaration in question in the code below, and since the compiler doesn't go on strike now even if I still haven't forward-declared the QPushButton.

Why is The QLabel more sensitive than QPushButton?

#ifndef INCOMEHANDLER_H
#define INCOMEHANDLER_H
 
#include <QDialog>
 
class QLabel; //With this row my prorgam compiles, without it i get the error posted above.
 
class IncomeHandler : public QDialog
{
	Q_OBJECT
 
	public:
		IncomeHandler(QWidget *parent = 0);
	signals:
 
	private slots:
	void okClicked();
 
	private:
		QLabel *activeLabel;
		QPushButton *okButton;
 
};
 
#endif

#ifndef INCOMEHANDLER_H
#define INCOMEHANDLER_H

#include <QDialog>

class QLabel; //With this row my prorgam compiles, without it i get the error posted above.

class IncomeHandler : public QDialog
{
	Q_OBJECT
	
	public:
		IncomeHandler(QWidget *parent = 0);
	signals:

	private slots:
	void okClicked();
	
	private:
		QLabel *activeLabel;
		QPushButton *okButton;

};

#endif

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