Re: dynamically growing 2D aray of structues

[Chris Moller <moller mollerware com>]

On 11/26/09 12:23, Ian Liu wrote:
> You can always map a 2d coordinate intto 1d:
> (i, j) -> i * w + j
> where w is the width of the matrix

That works poorly for dynamic arrays--every time you resize the array, 
in either dimension, you basically have to copy all the elements to new 
locations.

The general solution to multidimensional arrays in C is to use arrays of 
pointers:

ptr0 ->  e00 ee1 e02 e03 e04...
ptr1 ->  e10 e11 e12 e13 e14...
ptr2 ->  e20 e21 e22 e23 e24...
ptr3 ->  e30 e31 e32 e33 e34...
  .
  .
  .

This makes resizing fairly efficient--using reallocs--and can be 
implemented using GArray



> Ian L.
>
> On Thu, Nov 26, 2009 at 3:04 PM, <mauede alice it 
> <mailto:mauede alice it>> wrote:
>
>     As far as I know a GArray grows an array of pointers in 1D not 2D.
>     I thought of a GArray myself but my question, although not clear, is
>     how can I use a GArray to grow a 2D array of structures ?
>     Can you please provide an example ?
>
>
>     Thank you in advance,
>     Maura
>
>     -----Messaggio originale-----
>     Da: tristan van berkom gmail com
>     <mailto:tristan van berkom gmail com> per conto di Tristan Van Berkom
>     Inviato: gio 26/11/2009 6.31
>     A: mauede alice it <mailto:mauede alice it>
>     Cc: gtk-list gnome org <mailto:gtk-list gnome org>
>     Oggetto: Re: dynamically growing 2D aray of structues
>
>
>     On Wed, Nov 25, 2009 at 9:17 PM, <mauede alice it
>     <mailto:mauede alice it>> wrote:
>     > I dare ask for some guidelines as I am not a programmer and
>     never came
>     > across glib before.
>     > At the time being I have to embed some code into a package
>     (Galopps: a
>     > Genetic Algorithm) which is totally implemented in C language.
>     > To be consistent with Galopps style I have to use glib functions.
>     > I have just started to use the simplest glib primitives and data
>     types.
>     > Now I am stuck with the following problem. I know there are a
>     lot of experts
>     > out there who can give me a couples of hints.
>     > I have to generate a 2D array of structures which grows
>     dynamically in both
>     > directions.
>     > The structure is defined as follows:
>     >
>     > typedef struct {
>     >         gchar *id;
>     >         gchar *description;
>     >         gchar *sequence;
>     >         gint sequence_len;
>     >  } fasta_sequence;
>     >
>
>     Use a GArray:
>     http://library.gnome.org/devel/glib/stable/glib-Arrays.html
>
>     Cheers,
>           -Tristan
>
>     >
>     > Any suggestion is welcome.
>     > Thank you in advance,
>     > Maura
>     >
>     >
>     >
>     >
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