[Beowulf] Stroustrup regarding multicore

Perry E. Metzger perry at piermont.com
Tue Aug 26 14:25:43 EDT 2008


Kyle Spaans <kspaans at student.math.uwaterloo.ca> writes:
> Either way, I've recently started writing Conway's Game of Life in
> C, as an exercise. I needed to figure out how to dynamically
> allocate a 2D array. I found an answer on the comp.lang.c FAQ[1].
> It's not terribly complex, but it seems to me like it's more
> involved than with Fortran.

It is pretty easy, as easy as Fortran. I'm not sure I understand the
issue. Lets say you have a 100*100 array type...

typedef double my_array_t[100][100]

If you have a function, and you only want the thing
allocated for the life of that function...

int foo(blah...)
{
        my_array_t bar;

        ....
}

Or of course, you can just do it without an advance type declaration...

int foo(blah...)
{
        double bar[100][100];

        ....
}

If you don't know the size in advance, and you're just allocating for
the life of a function:

int foo(int dim_a, int dim_b,....)
{
        double bar[dim_a][dim_b]

}

works just fine (and indeed, you can use variables like that in any
block scope, not just at the start of a function block).

If you wish to allocate a my_array_t with malloc, it isn't really an
issue either.

ptr = malloc(sizeof(my_array_t))

Of course, if you don't know in advance how large your array is going
to be, you have to multiply, for example:

ptr = malloc(sizeof(double)*100*100)

> And if it came to an array of dimension >> 3, wouldn't that be a lot
> of array indicies and deferences to calculate as the dimensions
> added up.

C compilers are no worse than Fortran compilers at that.


-- 
Perry E. Metzger		perry at piermont.com
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