Re: Looking for a design pattern
* Michael Doubez:
On 10 ao?t, 23:52, Jerry Coffin <jerryvcof...@yahoo.com> wrote:
In article <4a808b83$0$426$426a7...@news.free.fr>,
michael.dou...@free.fr says...
[ ... ]
The idiomatic
choice for those who have made some editors from scratch (not just using
an edit control/widget).Look up "cursor gap" in Wikipedia or wherever.
I had a look on wikipedia ... as clear as the bottom of my socks.
The idea is pretty simple, really. When you're editing a text file,
you separate the file into two pieces: everything that's before the
cursor, and everything that's after the cursor.
That I understood but what do you gain except an amortized copy ?
I guess it is memory cost effective.
It's a *simple* structure that yields O(1) insertion and deletion at the cursor
position and O(1) random access read and write, where the former is the same as
with a linked list, and the latter is much better than a linked list.
The main cost is that, without reallocation and copying of all the data, the
maximum size of the buffer is determined up front, and it uses that much memory
regardless of the amount of data (for an editor, text), so no, it isn't
especially memory cost effective. :-)
Of course, in C++ any complexity for a more complicated structure can be hidden
under a simpler programmatic interface. So I guess that my comment reflected
that since C++ displaced C for such tasks, implementing editors from scratch
hasn't been that much in vogue. And the only such editor I made that I still
have the source code for, on magnetic tape, an editor for the HP3000 from 198x!,
wasn't written in C but in Pascal, and it didn't use cursor gap but a more
sophisticated list of blocks, sort of like a C++ std::deque implementation.
Cheers,
- Alf