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From: Malcolm Kay <malcolm.kay@internode.on.net>
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To: Henrik W Lund <henrik.w.lund@broadpark.no>,
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cc: ckorves@hotmail.com
Subject: Re: segmentation fault-- is my array too long?
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On Friday 07 May 2004 06:42, Henrik W Lund wrote:
....
> malloc() is your friend! :-)
>
> --> double *ncost = malloc(sizeof (double) * persons * scens); <--
>
> This ought to do the trick. Just remember to make sure that malloc
> returns a valid pointer, otherwise you'll have another seg fault.
>
> I'm pretty sure you can adress the pointer like you do with the array
> there (ncost[persons][0], etc...); if not, you can always do
> ncost(sizeof(double) * persons + 0), etc...
>
> /* AMENDMENT!!! */
> In my haste, I totally forgot my pointer dereferencing. The correct way
> to reference a pointer as a two dimensional array is, of course, thus:
>
> *(ncost + (sizeof(double) * persons) + 0)) = 0.00;

You've still got it wrong!
ncost increments in units of size equal to that which it points
so it should be:
  *(ncost + person*scens + scen)
where person is the first index and scen the second.
or in the particular instance
  *(ncost + person*scens + 0) = 0.00;

For easier to read code it would be better to use:
   double (*ncost)[scens] = malloc( persons * sizeof *ncost );

and dereference as:
   ncost[person][scen]

or in particular
   ncost[person][0] = 0.0;

And for the OP it is usual to write constants generated
with #define in upper-case. It generally seems to help
to make the code easier to follow. In this case:
 PERSONS instead of persons
and
 SCENS instead of scens

This also make the distinction between PERSONS and person
more evident while retaining their implied connection.

Malcolm