public member function
<unordered_set>
| container iterator (1) |
const_iterator cbegin() const noexcept;
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| bucket iterator (2) |
const_local_iterator cbegin ( size_type n ) const; |
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Return const_iterator to beginning
Returns a const_iterator pointing to the first element in the unordered_set container (1) or in one of its buckets (2).
A 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 iterator retrieved points to the first element of a bucket, otherwise it points to the first element of the container.
Member type size_type is an unsigned integral type.
Return Value
A const_iterator to the first element in the container (1) 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
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// 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;
}
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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:
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Iterator validity
No changes.