Erasing element from a vector – rbegin() vs begin() [duplicate] - c++

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How to call erase with a reverse iterator
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I'm trying to solve a problem in C++, a part of which requires me to erase elements from a vector using the rbegin() member function. However, the compiler throws an error every time I write the below-mentioned code. What's wrong here?
int main() {
int a = 1, b = 2;
vector<int> V = {a, b};
auto it = V.rbegin();
V.erase(it);
return 0;
}
It compiles just fine, however, if I access the same element using the begin() member function. The code below works fine.
int main() {
int a = 1, b = 2;
vector<int> V = {a, b};
auto it = V.begin()+1;
V.erase(it);
return 0;
}

Answer 1

There is no std::vector::erase() overload for reverse_iterator. However, you can obtain the corresponding iterator from a reverse_iterator by calling its base() member function:
auto rit = V.rbegin();
auto it = rit.base();
V.erase(it);
This code does compile but results in undefined behavior because the iterator counterpart of rbegin() corresponds to end(). From std::vector::erase() documentation:
iterator erase(const_iterator pos);
The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferencable) cannot be used as a value for pos.
rbegin().base() returns end(), not end() - 1. Nevertheless, you can advance rbegin() by one if you want a dereferencable iterator:
auto it = (std::next(rit)).base();