How can I iterate through a string and also know the index (current position)?

Often when iterating through a string (or any enumerable object), we are not only interested in the current value, but also the position (index). To accomplish this by using string::iterator we have to maintain a separate index:

string str ("Test string");
string::iterator it;
int index = 0;
for ( it = str.begin() ; it < str.end(); it++ ,index++)
{
    cout << index << *it;
}

The style shown above does not seem superior to the 'c-style':

string str ("Test string");
for ( int i = 0 ; i < str.length(); i++)
{
    cout << i << str[i] ;
}

In Ruby, we can get both content and index in a elegant way:

"hello".split("").each_with_index {|c, i| puts "#{i} , #{c}" }

So, what is the best practice in C++ to iterate through an enumerable object and also keep track of the current index?