Detect if iterator is last element of std::map

Question

This is similar to this question but not a duplicate. I'm trying to iterate through a map and print the values of each element, but with slightly different output on the last element. In that question, they recommend using map.rbegin().base(), but it's not working for me.

Here is my code:

#include <iostream>
#include <map>

int main()
{
    std::map <char, int> charMap = { {'a', 1}, {'b', 2}, {'c', 3}, {'d', 4} };
    for (auto iter = charMap.begin(); iter != charMap.end(); iter++)
    {
        std::cout << iter->first << ":\t" << iter->second;
        if (iter == charMap.rbegin().base())
            std::cout << "\t//This is the last element.\n";
        else
            std::cout << "\n";
    }
}

I'd expect my output to look like this:

a:    1
b:    2
c:    3
d:    4    //This is the last element. 

But instead, I am getting this output:

a:    1
b:    2
c:    3
d:    4    

Now I realize that there is a better way to do this, but I would expect this to work also. Why can't I compare iter and charMap.rbegin().base()?

Answer 1

Use std::next from <iterator> as

if (std::next(iter) == charMap.end())
    std::cout << "\t//This is the last element.\n";

instead.