Re: [Dev-C++] run time errors with big arrays

[<wa...@wa...>]

On 27 Feb 2004 at 0:16, risto holopainen wrote:

> Initialising arrays of large size seems to be a problem - the programs
> are compiled without warnings, but if the array (or multidimensional
> array) exceeds some specific size, the program crashes. Has anyone of
> you had the same problem, and is there anything to fix that? A related
> question that I have not found answered in my programming textbooks:
> How is a multidimensional array dynamically initialised? In other
> words, this works:
>   double *ar;
>   ar = new double[10];
> but what is the correct syntax for initialising for example ar[10][10]
> with new?

The problem is that the C and C++ memory models are different.

C++ sees something like double ar[10][10] and builds that on the 
stack.  You quickly run out of space and start stepping on things 
that way.  I had the same problem when I came from C to C++ (a short 
time ago.)

So, you should either consider using vectors or set it up as a 
pointer to pointers (double **ar) and then initialize it like:

// init 10 pointers to double.
ar = new double *[10];

// init each pointer to double to a pointer to double.
for (int i=0; i < 10; i++)
   ar[i] = new double[10];

At least... that's the way I've been doing it but I'm still new to 
C++.

Oh, and be sure to delete them when you're done.


HTH.

Watson (the pencil neck) Davis