Re: Segmentation Fault

On Tue, 1 Sep 2009 22:08:16 UTC, Nobody <nobody@xxxxxxxxxxx> wrote:

On Tue, 01 Sep 2009 22:57:48 +0100, Rahul wrote:

I believe my code is correct and caches all results in an Array for
efficiency (only look up is needed). But it generates a Segmentation Fault
everytime I run it.

Can anyone see what the problem is?

static bool squares[INT_MAX]; // automatically initialized to 0, no

You shouldn't assume that you will be able to allocate an array this
large (on a 32-bit system, INT_MAX is typically 2^31-1, which would
require at least 2GiB of memory).

setupsquares ()
{
int i;
for(i = 0; i < INT_MAX; squares[i * i++] = true);

If i can go up to INT_MAX-1, then i*i can go up to (INT_MAX-1) squared,
which is outside the bounds of the array. But you almost certainly won't
be able to allocate an array that large (for INT_MAX == 2^31-1,
that's approximately 4 Exabytes).


It doesn't matter because i*i++ is undefined behavior twice!

i*i gives overflow and overflow of int is not defined

i*i++ itself is undefined behavior as the side effect on ++ is againxt
the rule that accessing the variable i more than once while ++ is in
that statement - so anything is broken.


--
Tschau/Bye
Herbert

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