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Returns an iterator pointing to the first element in the unordered_set container (1) or in one of its buckets (2).
Notice that an unordered_set object makes no guarantees on which specific element is considered its first element. But, in any case, the range that goes from its begin to its end covers all the elements in the container (or the bucket), until invalidated.
All iterators in an unordered_set have const access to the elements (even those whose type is not prefixed with const_): Elements can be inserted or removed, but not modified while in the container.
All return types (iterator, const_iterator, local_iterator and const_local_iterator) are member types. In the unordered_set class template, these are forward iterator types.
Possible output:
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
<unordered_set>
-
unordered_multisetC++11
-
unordered_setC++11
unordered_set
-
unordered_set::~unordered_setC++11
-
unordered_set::unordered_setC++11
member functions
-
unordered_set::beginC++11
-
unordered_set::bucketC++11
-
unordered_set::bucket_countC++11
-
unordered_set::bucket_sizeC++11
-
unordered_set::cbeginC++11
-
unordered_set::cendC++11
-
unordered_set::clearC++11
-
unordered_set::countC++11
-
unordered_set::emplaceC++11
-
unordered_set::emplace_hintC++11
-
unordered_set::emptyC++11
-
unordered_set::endC++11
-
unordered_set::equal_rangeC++11
-
unordered_set::eraseC++11
-
unordered_set::findC++11
-
unordered_set::get_allocatorC++11
-
unordered_set::hash_functionC++11
-
unordered_set::insertC++11
-
unordered_set::key_eqC++11
-
unordered_set::load_factorC++11
-
unordered_set::max_bucket_countC++11
-
unordered_set::max_load_factorC++11
-
unordered_set::max_sizeC++11
-
unordered_set::operator=C++11
-
unordered_set::rehashC++11
-
unordered_set::reserveC++11
-
unordered_set::sizeC++11
-
unordered_set::swapC++11
-
non-member overloads
-
operators (unordered_set)C++11
-
swap (unordered_set)C++11
-
public member type
<unordered_set>
std::unordered_set::begin
container iterator (1) | iterator begin() noexcept;const_iterator begin() const noexcept; |
---|---|
bucket iterator (2) | local_iterator begin ( size_type n );const_local_iterator begin ( size_type n ) const; |
Return iterator to beginning
Notice that an unordered_set object makes no guarantees on which specific element is considered its first element. But, in any case, the range that goes from its begin to its end covers all the elements in the container (or the bucket), until invalidated.
All iterators in an unordered_set have const access to the elements (even those whose type is not prefixed with const_): Elements can be inserted or removed, but not modified while in the container.
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
An iterator to the first element in the container (1) or the bucket (2).All return types (iterator, const_iterator, local_iterator and const_local_iterator) are member types. In the unordered_set class template, these are forward iterator types.
Example
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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: |
Complexity
Constant.Iterator validity
No changes.See also
- unordered_set::end
- Return iterator to end (public member type)
- unordered_set::cbegin
- Return const_iterator to beginning (public member function)
- unordered_set::find
- Get iterator to element (public member function)
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Spotted an error? contact us