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List:       kde-devel
Subject:    Re: Hex editor widget
From:       "Friedrich W. H.  Kossebau" <Friedrich.W.H () Kossebau ! de>
Date:       2003-06-22 10:48:50
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Am Samstag, 21. Juni 2003 17:37 schrieb Gerold J. Wucherpfennig:
> On Saturday 21 June 2003 00:45, Russell Miller wrote:
> > I would also be interested in such a widget - one of the apps that I have
> > written, kbview, would benefit greatly from such a widget.  What I would
> > like to see (not a list of demands, but a list of wishes):
> >
<snip 1-6>

> 7. On demand loading - don't load the whole file at once.
>    This is needed to work with huge files.

Also this had been in my mind when introducing the data abstraction layer (I 
called KDataBuffer, anyone a better name?). As this is a special need it 
should be implemented on a per-app base I think (although I wouldn't mind if 
someone comes up with a general pattern class for this :)
But I still have no real clue how to support an on-demand loading in the API 
of the layer. I thought of something like a call 
  prepareRange( Offset, Length )
where the actual working range (whatever this defines) is ensured to be loaded 
and accessable in memory by call to data()/datum().

Does anyone know of a design pattern for this?

FWIW here is my actual draft:

class KDataBuffer
{
  public:
    KDataBuffer();
    virtual ~KDataBuffer();

  public:
    int size() const;

  public:
    /** locates working range, returns false if failed */
    virtual bool prepareRange( int Offset, int Length ) = 0;
    /** expects pointer to memory, should be in prepared range */
    virtual const char *data( int Offset, int Length ) = 0;
    /** */
    virtual const char datum( int Offset ) = 0;
    /** is the buffer changeable ?*/
    virtual bool isReadOnly() const = 0;
    /** is the buffer resizeable ?*/
    virtual bool isResizeable() const = 0;

    /** inserts at Position */
    virtual int insert( const char*, int Length, int Pos = 0 ) = 0;
    /** removes beginning with position as much as possible, returns length of 
removed */
    virtual int remove( int Pos, int Length ) = 0;
    /** replaces as much as possible, returns length of substituted */
    virtual int replace( const char*, int Length, int Pos ) = 0;

    /** searches beginning with byte at Pos, returns -1 if nothing found */
    virtual int find( const char*, int Length, int Pos = 0 ) = 0;
    /** searches backward beginning with byte at Pos, returns -1 if nothing 
found */
    virtual int rfind( const char*, int Length, int Pos = -1 ) = 0;

/*     virtual int find( const QString &expr, bool cs, bool wo, bool forward = 
true, int *index = 0 ); */

  protected:
    /** size of the data */
    int Size;
};

Friedrich

 
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