Return a const iterator to the first element, or cend if empty.
Declared in <bslstl_set.h>
set<KEY, COMPARATOR, ALLOCATOR>::const_iterator
cbegin() const noexcept;Return an iterator providing non-modifiable access to the first value_type object in the ordered sequence of value_type objects maintained by this set, or the cend iterator if this set is empty.
const iterator to the first element, or cend()