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Exception handling C++ and Qt

 
 
Michael Doubez
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      02-10-2011
On 9 fév, 17:32, "Ady" <(E-Mail Removed)> wrote:
> "Michael Doubez" <(E-Mail Removed)> wrote in message
> >
> > news:(E-Mail Removed)....
> > On 8 fév, 17:37, "Ady" <(E-Mail Removed)> wrote:
> > [snip]
> >
> > > I am writing an application using Nokias Qt Creator on Windows and C++
> > > (because it's free) which is intended to examine the contents of a data
> > > file
> > > byte-by-byte and generating an output of byte, short int and long int
> > > values
> > > depending on the position of what the user has selected. All this works.
> > > However, when I try to add a QDateTime variable to the program and I move
> > > the relevant data segment to the variable, then try to use the .isValid()
> > > function I always get an access violation which Qt can't handle.

> >
> > > I know I'm doing something daft here, and I'm quite new to C++. If anyone
> > > can point me in the right direction it would be appreciated.

> >
> > No it is not. serialization is actually quite common.
> >
> > > I am posting the relevant section of code.

> >
> > [snip: code]
> >
> > The read code is not *sufficient, you should also post how you wrote
> > the file.
> >
> > Quickly reading the Qt documentation, I notice there is a QDataStream
> > class used for (de)serializing data. May be you can use it for writing/
> > > reading your file.

> >

>
> I feel some further explanation is required here. My program was originally
> intended to emulate the DUMP command from the OpenVMS operating system (my
> day job) on a Windows box. That bit of the program works so I decided to
> extend it allow the user to examine the contents of the file - ANY file. It
> may be a formatted file, it might not, it's whatever the user decides to
> look into. It's a tool I've found useful over the years.
>

[snip]
>
> In answer to your post, there is therefore no writing of the original file.
> The file is selected by the user, opened, read into an appropriately sized
> buffer (malloc'd) and closed. The data is displayed in a hex dump window and
> a Ascii window (if a printable character). The user can then click or
> double-click on any byte displayed in the hex dump and the values of the
> various simple data types are displayed. I was hoping to add a date type but
> this is where I'm getting the access violations.


IIRC you have a binary dump of your memory.

> If there is a simple way of translating a 64-bit date 'type' under Qt I
> would really like to see it. It doesn't seem to have anything like the
> SYSTEMTIME and FILETIME structures that are available under VC++ 6.


SYSTEMTIME and FILETIME are C structure (POD in C++). As Richard
pointed out, QDateTime is not POD. Looking into QT headers, it seems
QtDate Time is composed of a QDate and a QTime but QDate, at least,
has virtual functions. This means the layout of the class may include
additional (RTTI) data and/or member layout reorganisation.

In short, the internal joined data is 64 bits (depending on compiler's
paddings) but there should also be a vtable pointer somewhere causing
the access violation you get; this is also plateform specific.

A solution could be to interpret your 64 bits into two unsigned int
and use them to initialise a QDateTime structure.

--
Michael
 
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Ady
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      02-10-2011
Michael,

Thanks for the pointers, I'll look into it.

Ade


 
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