Question

What is the behavior of std::advance when you have say:

std::vector<int> foo(10,10);
auto i = foo.begin();
std::advance(i, 20);

What is the value of i? Is it foo.end()?

Answer 1

You are passing the foo size by advancing to 20th position. Definitely it is not end of the vector. It should invoke undefined behavior on dereferencing, AFAIK.

Edit 1:

#include <algorithm>
#include <vector>
#include <iostream>

int main()
{
     std::vector<int> foo(10,10) ;
     std::vector<int>::iterator iter = foo.begin() ;
     std::advance(iter,20);

     std::cout << *iter << "\n" ;

     return 0;
}

Output: 0

If it is the vector’s last element, then it should have given 10 on iterator dereferencing. So, it is UB.

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