[Interest] QSettings: is a group present? Crash with qWarning.

Thiago Macieira thiago.macieira at intel.com
Fri Aug 24 08:59:16 CEST 2012

On sexta-feira, 24 de agosto de 2012 08.04.49, Sensei wrote:
> But the real problem is this: why is the documentation referring to 
> bool, and not to QBool?
>         http://qt-project.org/doc/qt-4.8/qstringlist.html#contains
>         bool QStringList::contains ( const QString & str,
> Qt::CaseSensitivity  cs = Qt::CaseSensitive ) const
> Actually, the header refers to QBool, as you correctly point out:
>         inline QBool contains(const QString &str, Qt::CaseSensitivity cs = 
> Qt::CaseSensitive) const;
> So there's a "bug" in the docs... am I right?

No. It's not a bug if it's intentional.

QBool is a hidden class that is actually a bool. In most cases, you don't 
realise it's there because it casts automatically to bool. The two cases that 
it won't do are in ... passing and in template matching.

Qt 4 has been using QBool for 7 years and you're the first person who has come 
to this error, so I don't think it's a real issue (and you probably ignored a 
compiler warning).

QBool exists to mark a function that returns a boolean in Qt 4, but returned 
an int in Qt 3. It exists to make sure you're not treating the return value 
like it was done in Qt 3. E.g.:

	QString foo("hello hello");
	if (foo.contains("hello") > 1) { ... }

The above was valid in Qt 3 but in Qt 4 it should error out. If the function 
returned boolean, it would compile but it would be always false.

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
     Intel Sweden AB - Registration Number: 556189-6027
     Knarrarnäsgatan 15, 164 40 Kista, Stockholm, Sweden
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