Vector iterators

Question

I have a the following code.

vector* irds = myotherobj->getIRDs();//gets a pointer to the vector
for(vector::iterator it = ir         


        

Answer 1

First consider whether you actually need a pointer to the element or if you're just trying to kind of use iterators but kind of avoid them. It looks like you're trying to code C in C++, rather than coding C++. In the example you gave, it seems like rather than converting to a pointer and then working with that pointer, why not just use the iterator directly? it->doSomething() instead of ird->doSomething().

If you're thinking that you need to save that pointer for later to use on the vector after doing some work, that's potentially dangerous. Vector iterators and pointers to elements in a vector can both be invalidated, meaning they no longer point to the vector, so you are basically attempting to use memory after you've freed it, a dangerous thing to do. A common example of things that can invalidate an iterator is adding a new element. I got into the mess of trying to store an iterator and I did a lot of work to try to make it work, including writing a "re_validate_iterator()" function. Ultimately, my solution proved to be very confusing and didn't even work in all cases, in addition to not being scalable.

The solution to trying to store the position of the vector is to store it as an offset. Some integer indicating the position within the vector that your element is at. You can then access it with either myvector.begin() + index if you need to work with iterators, or myvector.at (index) if you want a reference to the element itself with bounds checking, or just myvector [index] if you don't need bounds checking.