Array out of bounds?

[SJ]

I've came across this today

c++:

vector <int> v;     v.push_back (5);     // version1, this doens't give an error     for (int i = 0; i+2 < v.size(); i++)       cout << v[i+2] << endl;         // version2, this goes nuts!     for (int i = 0; i < v.size()-2; i++)       cout << v[i+2] << endl;

version 1 seem to ignore the out of bounds element, whereas version 2 print out a bunch of random numbers then freeze up. I would predict a segmentation fault for both cases, but why does the first one just (seemingly) ignore it?

[A.J]

Keep in mind that you only pushed 1 element (namely '5'). So, v.size() will return 1.

Version 1 exits when i + 2 >= v.size(). But since i = 0, and v.size() = 1, it doesn't output anything (because i + 2 > v.size() ).

Although in Version 2, you want i >= v.size() - 2 for the loop to exit.....however, since i = 0 initially and v.size() - 2 = -1, the loop goes on forever (because i increases by 1, and therefore can never by less than or equal to -1)

That's why it crashes....

[SJ]

ahh right, thank you

[A.J]

no probs

[md]

Errm... 0 >= -1 so the second loop should exit right away... this is one of those times a debugger might help - or not waking up at 3:00 pm...