CODEWITHSUNDEEP
c++vectoriterator
smdsmkd
smdsmkd

Reputation: 41

check which vector an iterator belongs to

I have 3 iterators which belong to 3 vectors A, B and C. A function minn is called with these 3 iterators which returns the iterator with minimum value. Now how can i know which vector does the returned iterator minit belongs to? code -

vector<int>::iterator a = A.begin(), b = B.begin(), c = C.begin();
auto minit = minn(a,b,c);

Upvotes: 3

Views: 488

Answers (2)

Caleth
Caleth

Reputation: 62719

The easiest option would be to not pass these iterators by value, so when you modify minit, whichever of a, b or c was chosen also changes.

bool itLess(std::vector<int>::iterator& l, std::vector<int>::iterator& r)
{
    return *l < *r;
}

for (
    auto a = A.begin(), b = B.begin(), c = C.begin(); 
    a != A.end() && b != B.end() && c != C.end();
    )
{
    auto [minit, maxit] = std::minmax({std::ref(a), std::ref(b), std::ref(c)}, itLess);
    // use minit.get() and maxit.get()
}

See it on coliru

Upvotes: 1

Piotr Siupa
Piotr Siupa

Reputation: 4838

We can take advantage of the fact that vector stores its elements in a single continuous array. We can check if the element pointed by the iterator is located in memory between the beginning and the end of that array.

template<typename T>
bool isFromVector(const typename std::vector<T>::const_iterator &i, const std::vector<T> &v)
{
    const T *const dataBeginning = v.data();
    const T *const dataEnd = v.data() + v.size();
    const T *const element = &*i;
    return std::less_equal<const T*>()(dataBeginning, element) && std::greater<const T*>()(dataEnd, element);
}

Upvotes: 0

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