Possible causes for strange vector display?

[dudeomanodude]

In my code I have a vector that should be a size of 1, containing the integer value 2.

When this portion of the code runs:

std::cout << "Root size: " << root->key.size() << "\n";

typename std::vector<T>::iterator it = root->key.begin();
for(; it != root->key.end(); ++it){
    std::cout << *it << " ";
}

and the output is as I expect:

Root size: 1
2

But when I have this in my code:

Node* curr = root;
std::cout << curr->key[0] << "\n";
std::cout << curr->key[1] << "\n";
std::cout << curr->key[2] << "\n";

This is the output:

2
2
0

So what's with the extra "2" in the output?

Is it because operator[] returns a reference and perhaps it's referencing some erroneous data? I'm confused because the size() is correct and the iterator display works correctly...

I'm preplexed...

BTW: replacing curr->key[x] with root->key[x] makes no difference, curr doesn't point to anything else in the function either.

[Daved]

The operator[] does not do any bounds checking, so by accessing elements at the indexes 1 and 2, you are invoking undefined behavior and probably just getting whatever random values are in memory at that location.

The solution is to never pass operator[] anything outside of the range [0, size-1].

[matsp]

Just typical undefined behaviour - you are accessing a vector as an array, and accessing it out of bounds - if you use at() instead of operator[], you will get an exception thrown when you go out of bounds. The operator[] access method for std::vector is "undefined" for access beyond the size, and "anything" can happen.

See: http://cpwiki.sourceforge.net/Undefined_behaviour

--
Mats

[dudeomanodude]

Thanks guys.