What are the scenarios when do..while is used?

Question

I'm curious as to why libstdc++ is using a RB-tree to implement std::set (details here
https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/std/set and here https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/include/bits/stl_tree.h ),
when there are faster alternatives?

I'm mainly curious, because from all the people I've asked there hasn't been a single answer in favor of RB-trees, other than "they're already popular" or "easy to implement".

If you'd like more details on that, here's a link to my question on stackexchange http://cs.stackexchange.com/questions/41969/why-are-red-black-trees-so-popular,
where nobody has yet answered as well.

Using a variant of B-tree (or (a,b)-tree) should be faster, and everyone seems to suggest so, which makes me wonder what is the reason for picking RB-trees? This is not a question about their theoretical speed, but about real world behavior on real hardware with respect to CPU caches, etc.

Answer 1

A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time.

Syntax

do {
 body of loop; 
} while ( test expression );

Answer 2

In addition to the Salil Agrawal's ans
You can use do { } while (); when you wnated that your code must be executed irrespective of the conditon i.e (while (condition)), atleast one time.
Then you can use do..while in that scenarios.