• simendsjo (19/19) Aug 07 2010 I understand this is an unsafe operation, I just have a quick question.
• bearophile (5/7) Aug 07 2010 Generally it contains "garbage".
• simendsjo (2/9) Aug 08 2010 Ok, thanks. I expected this, but It's good to get it verified.
• div0 (8/10) Aug 07 2010 Yes. It's entirely undefined what will happen, you might find that the

simendsjo <simen.endsjo pandavre.com> writes:

I understand this is an unsafe operation, I just have a quick question.


Here, b points outside a's memory, so I get garbage.
	{
		int[] a = [3,3,3];
		auto p = a.ptr;
		auto b = p[0..3];
		assert(b == [3,3,3]);
		b = p[0..4]; // b == [3,3,3,?]
	}


When I do the same with a static array, I get 0. But this is just 
actually garbage, right? It might contain other data, and not always 0?

	{
		int[3] a = [3,3,3];
		auto p = a.ptr;
		auto b = p[0..3];
		assert(b == [3,3,3]);
		b = p[0..4];
		assert(b == [3,3,3,0]);
	}

bearophile <bearophileHUGS lycos.com> writes:

simendsjo:
 When I do the same with a static array, I get 0. But this is just 
 actually garbage, right? It might contain other data, and not always 0?

Generally it contains "garbage".
In string literals there is one more item that's empty (zero). I don't know if
normal fixed-sized arrays too have the extra leading zero item (maybe yes), but
relying on it is surely bad programming practice.

Bye,
bearophile

simendsjo <simen.endsjo pandavre.com> writes:

On 07.08.2010 16:48, bearophile wrote:
 simendsjo:
 When I do the same with a static array, I get 0. But this is just
 actually garbage, right? It might contain other data, and not always 0?

 Generally it contains "garbage".
 In string literals there is one more item that's empty (zero). I don't know if
normal fixed-sized arrays too have the extra leading zero item (maybe yes), but
relying on it is surely bad programming practice.

 Bye,
 bearophile

Ok, thanks. I expected this, but It's good to get it verified.

div0 <div0 sourceforge.net> writes:

On 07/08/2010 13:45, simendsjo wrote:
 When I do the same with a static array, I get 0. But this is just
 actually garbage, right? It might contain other data, and not always 0?

Yes. It's entirely undefined what will happen, you might find that the 
extra bit of memory you try and access is a non readable page which will 
give you a seg fault or it could be any random chunk of data depending 
on how the executable gets linked.

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