CODEWITHSUNDEEP
c++stliterator
amigo421
amigo421

Reputation: 2541

is iterator end() of the container

Is there a way to check that iterator (passed to function as parameter "last") is equal to end() in case I haven't the container itself?

template<typename ForwardIterator>
void MyFunc(ForwardIterator first, ForwardIterator last) {
...
}

Upvotes: 1

Views: 220

Answers (2)

Damon
Damon

Reputation: 70126

Normally, MyFunc should consider the range including first and excluding last just as the standard algorithms do, too.

Which is done in the standard library for the exact reason (or problem) that you are stating. Typical calls to algorithm functions that take e.g. an entire container look like algoname(foo.begin(), foo.end()); where foo.end() is an iterator that points to an invalid element after the last valid one. The algorithm would thus need to somehow know whether it can dereference any given iterator (or, at the very least, the one given in last).

On the other hand, the problem is entirely avoided by defining that last is exclusive. So, for example iterating over the elements can be done in terms of for(... it != last), and this same code will work for any and every value of last, both ones that refer to valid objects, and the one returned by end(). The only thing the implementation needs to make sure is that first <= last, and nothing can go wrong.

Upvotes: 1

pdeschain
pdeschain

Reputation: 1421

AFAIK - no. If you don't have the container, you can't get the ::end() iterator, thus you can't do the comparison. Why not pass the container as reference?

Check out: Testing whether an iterator points to the last item?

Upvotes: 1

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