[Qt-interest] QFile private member

[Pete Christensen]

andrew.m.goth at l-3com.com wrote:
> Pete Christensen wrote:
>> OK, I give up, I can not do this. How do I declare a private member 
>> variable of type QFile and initialize it in the constructor?
> 
> Are you sure you want QFile and not QFile*?
> 
>> Compiler complains:
>> /usr/include/qt4/QtCore/qfile.h:191: error: 
>> 'QFile::QFile(const QFile&)' 
>> is private
> 
> The gripe is against the header file, not the implementation of the
> constructor.  Specifically the complaint is that the QFile copy
> constructor is private.  Why would that be a problem?  It looks to me
> that it's trying to make a default copy constructor for your class, but
> it can't since it would rely on copy constructors for all data members
> of your class.  You could explicitly define a copy constructor for your
> class, or you could just switch to QFile*, which can be copied without
> incident.
> 

OK, it's starting to make a little sense. I looked up "copy constructor".

"A copy constructor is generally needed when an object owns pointers or
non-shareable references, such as to a file, in which case a destructor
and an assignment operator should also be written."

So now I'm pretty sure QtCore does things like:

190 private:
191     Q_DISABLE_COPY(QFile)
192 };

(this from qfile.h) to explicitly get the compiler to barf in situations.

I'll look into this destructor/assignment operator thing.

Regarding subclassing, I'm not actually creating a new QFile type, this
was just the simplest I could get my code to communicate my problem.
Eventually I need to read the file in a thread.