std::unordered_set::cend

container iterator (1)	const_iterator cend() const noexcept;
bucket iterator (2)	const_local_iterator cend ( size_type n ) const;

Return const_iterator to end

Returns a const_iterator pointing to the past-the-end element in the unordered_set container (1) or in one of its buckets (2).

The

const_iterator returned by cend does not point to any element, but to the position that follows the last element in the unordered_set container or in one of its buckets (i.e., their past-the-end position). Thus, the value returned shall not be dereferenced - it is generally used to describe the open-end of a range, such as [cbegin,cend).

Notice that an unordered_set object makes no guarantees on which order its elements follow. But, in any case, the range that goes from its

cbegin to its cend covers all the elements in the container (or the bucket), until invalidated.

const_iterator is an iterator that points to const content. This iterator can be increased and decreased (unless it is itself also const), but it cannot be used to modify the contents it points to.

Parameters

n: Bucket number. This shall be lower than bucket_count.
It is an optional parameter that changes the behavior of this member function: if set, the const_iterator retrieved points to the past-the-end element of a bucket, otherwise it points to the past-the-end element of the container.
Member type size_type is an unsigned integral type.

Return Value

A const_iterator to the element past the end of the container (2) or the bucket (2).

Both

const_iterator and const_local_iterator are member types. In the unordered_set class template, these are forward iterator types.
They may both be aliases of the same iterator type.

Example

// unordered_set::cbegin/cend example
#include <iostream>
#include <string>
#include <unordered_set>

int main ()
{
  std::unordered_set<std::string> myset =
  {"Mercury","Venus","Earth","Mars","Jupiter","Saturn","Uranus","Neptune"};

  std::cout << "myset contains:";
  for ( auto it = myset.cbegin(); it != myset.cend(); ++it )
    std::cout << " " << *it;    // cannot modify *it
  std::cout << std::endl;

  std::cout << "myset's buckets contain:\n";
  for ( unsigned i = 0; i < myset.bucket_count(); ++i) {
    std::cout << "bucket #" << i << " contains:";
    for ( auto local_it = myset.cbegin(i); local_it!= myset.cend(i); ++local_it )
      std::cout << " " << *local_it;
    std::cout << std::endl;
  }

  return 0;
}

Possible output:

myset contains: Venus Jupiter Neptune Mercury Earth Uranus Saturn Mars
myset's buckets contain:
bucket #0 contains:
bucket #1 contains: Venus
bucket #2 contains: Jupiter
bucket #3 contains: 
bucket #4 contains: Neptune Mercury
bucket #5 contains: 
bucket #6 contains: Earth
bucket #7 contains: Uranus Saturn
bucket #8 contains: Mars
bucket #9 contains: 
bucket #10 contains:

Complexity

Constant.

Iterator validity