How do I check whether a reference is const?

Question

I was writing a test for my iterator types and wanted to check that the reference returned by de-referencing iterators provided by begin() and cbegin() are non-const and const respectively.

I tried doing something similar to the following : -

#include <type_traits>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> vec{0};

    std::cout << std::is_const<decltype(*vec.begin())>::value << std::endl;
    std::cout << std::is_const<decltype(*vec.cbegin())>::value << std::endl;
}

But this prints 0 for both cases.

Is there a way to check if a reference is const?

I can use C++11/14/17 features.

Answer 1

Remove the reference to get the referenced type to inspect its constness. A reference itself is never const - even though references to const may colloquially be called const references:

std::is_const_v<std::remove_reference_t<decltype(*it)>>