[Qt-interest] QFile private member

[Pete Christensen]

Scott Aron Bloom wrote:
> 
>> -----Original Message-----
>> From: qt-interest-bounces at trolltech.com [mailto:qt-interest-
>> bounces at trolltech.com] On Behalf Of Pete Christensen
>> Sent: 2009-02-10 13:32
>> To: qt-interest at trolltech.com
>> Subject: Re: [Qt-interest] QFile private member
>>
>> 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.
>> _______________________________________________
>> Qt-interest mailing list
>> Qt-interest at trolltech.com
>> http://lists.trolltech.com/mailman/listinfo/qt-interest
> [Scott Aron Bloom] 
> You are creating a new QFile, except by using QFile rather then QFile *.
> 
> Simply making it a QFile *, and then in the constructor, creating a
> blank QFile...
> 
> file = new QFile;
> 
> You will solve all your issues...
> 
> Scott
> 
> 

OK, cool. Andrew called it and Scott actually figured out that I know 
nothing about C++ and then told me how to assign an actual object to a 
pointer. (I think that's how to describe what's happening here.)

The other suggestions, including Andreas', using reference "file QFile" 
and not pointer "file * QFile" all fail to compile with the same error. 
I'm pretty sure I'd need an explicit copy constructor to get that to 
work. (And I'm finding there's nothing "plain" about C++, Andreas :))

Thanks guys. Hopefully I can actually figure out how to use this pointer 
I've now got.

Re: destructor: will-do, Bob.