[Qt-interest] How to save the content in tree structure to file

[Ramesh]

Andre.. Thanks..

I will see your idea


 

But I am thinking to do in XML format. 

Any way thanks lot

 

From: qt-interest-bounces at trolltech.com
[mailto:qt-interest-bounces at trolltech.com] On Behalf Of Andre Somers
Sent: Tuesday, May 04, 2010 4:24 PM
To: qt-interest at trolltech.com
Subject: Re: [Qt-interest] How to save the content in tree structure to file

 

Hi,

On 4-5-2010 11:39, Ramesh wrote: 

Ok.. I’m sorry,

 

I know how to use Qdatastream , which we use to write the data to file.. but
its not serialized..

QDataStream does data serialization. What do you mean if you say "it is not
serialized"?



The way you write is the same wy you need to access the data from the
system..

I have no idea what you mean by this. 



But in tree hierarchy, I need the key value pairs.. I need to know which one
is parent and child..

How can I do it.. by using Qdatastream?

You can use QDataStream to stream any file structure you like. QDataStream
does not do the structuring for you, unless the class you are streaming out
already contains such structure and it supports the QDataStream stream
operators << and >>, such as QList or QHash do. What do you mean by "the key
value pairs"? Which pairs? 

You don't talk about how your data is structured in your program.
Unfortunately, Qt does not supply a QTree<> container. So, I guess you are
using some other structure. Could you tell us what you have now?

I would probably do something according to these lines:
The first step is a format for the tree itself. I would choose to stream out
the number of items at top level in the tree as an unsigned int (quint32),
followed by each of the top level tree items. That is really all you need.

How each item looks exactly, depends on what data you want to store in each
tree item. In the example below, I will assume only a name that is stored in
a QString and an unsigned integer ID. Each tree item is then an instance of
a class, like this (all code is pseudo-code):

class TreeItem {
    unsigned int id;
    QString name;
    QList<TreeItem> children();
    unsigned int childCount();
}
    
If you want to write that to a file using QDataStream, you could do
something like this:

QDataStream operator()<<(QDataStream& out, const TreeItem& item) {
  out << quint32(item.id);
  out << item.name;
  out << quint32(item.childCount());
  foreach(TreeItem, item.children()) {
      out << item; // note: this is a recursive call!
  }
  return out;
}

That is, you have each TreeItem write out its own data, the number of its
children, and then recursively write out each of its children.

Reading back is the opposite process, where you need to be VERY CAREFULL
that the procedures work on exactly the same structure, with the same data
types. 

If you would considder not using QDataStream (you are not telling why you
want to use it), you could perhaps also considder the suggestion by Srdjan
to use XML. It still requires you to do your own reading and writing
somewhere, so I am not sure if it is a benefit for you. Personally, I think
XML is nice, but mainly if you:
* need to have the data sort-of human readable, or
* need to have interoperability and extensibility.

André




 

 

 

From: qt-interest-bounces at trolltech.com
[mailto:qt-interest-bounces at trolltech.com] On Behalf Of Andre Somers
Sent: Tuesday, May 04, 2010 3:01 PM
To: qt-interest at trolltech.com
Subject: ***SPAM*** Re: [Qt-interest] How to save the content in tree
structure to file

 

On 4-5-2010 11:25, Ramesh wrote: 

Hi,

 

I want to save the data to a file in tree hierarchy, Same way I want to
display it on UI.

 

How can I achieve that in Qt.. 

 

This question can not be answered the way you formulate it. 
Please read and understand http://catb.org/~esr/faqs/smart-questions.html
<http://catb.org/%7Eesr/faqs/smart-questions.html> , and reformulate your
question.

André

 

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