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C
C++
算法 | Algorithm
原子性操作 | Atomic operations
概念 | Concepts
容器 | Containers
cbefore_begin
Containers library
Node handle
operators (std::array)
operators (std::deque)
operators (std::forward_list)
operators (std::list)
operators (std::map)
operators (std::multimap)
operators (std::multiset)
operators (std::queue)
operators (std::set)
operators (std::stack)
operators (std::unordered_map)
operators (std::unordered_multimap)
operators (std::unordered_multiset)
operators (std::unordered_set)
operators (std::vector)
remove_if
remove_if
std::array
std::array::at
std::array::back
std::array::begin
std::array::cbegin
std::array::cend
std::array::crbegin
std::array::crend
std::array::data
std::array::empty
std::array::end
std::array::fill
std::array::front
std::array::max_size
std::array::operator[]
std::array::rbegin
std::array::rend
std::array::size
std::array::swap
std::deque
std::deque::assign
std::deque::at
std::deque::back
std::deque::begin
std::deque::cbegin
std::deque::cend
std::deque::clear
std::deque::crbegin
std::deque::crend
std::deque::deque
std::deque::emplace
std::deque::emplace_back
std::deque::emplace_front
std::deque::empty
std::deque::end
std::deque::erase
std::deque::front
std::deque::get_allocator
std::deque::insert
std::deque::max_size
std::deque::operator[]
std::deque::pop_back
std::deque::pop_front
std::deque::push_back
std::deque::push_front
std::deque::rbegin
std::deque::rend
std::deque::resize
std::deque::shrink_to_fit
std::deque::size
std::deque::swap
std::forward_list
std::forward_list::assign
std::forward_list::before_begin
std::forward_list::begin
std::forward_list::cbegin
std::forward_list::cend
std::forward_list::clear
std::forward_list::emplace_after
std::forward_list::emplace_front
std::forward_list::empty
std::forward_list::end
std::forward_list::erase_after
std::forward_list::forward_list
std::forward_list::front
std::forward_list::get_allocator
std::forward_list::insert_after
std::forward_list::max_size
std::forward_list::merge
std::forward_list::pop_front
std::forward_list::push_front
std::forward_list::remove
std::forward_list::resize
std::forward_list::reverse
std::forward_list::sort
std::forward_list::splice_after
std::forward_list::swap
std::forward_list::unique
std::get(std::array)
std::hash
std::list
std::list::assign
std::list::back
std::list::begin
std::list::cbegin
std::list::cend
std::list::clear
std::list::crbegin
std::list::crend
std::list::emplace
std::list::emplace_back
std::list::emplace_front
std::list::empty
std::list::end
std::list::erase
std::list::front
std::list::get_allocator
std::list::insert
std::list::list
std::list::max_size
std::list::merge
std::list::pop_back
std::list::pop_front
std::list::push_back
std::list::push_front
std::list::rbegin
std::list::remove
std::list::rend
std::list::resize
std::list::reverse
std::list::size
std::list::sort
std::list::splice
std::list::swap
std::list::unique
std::map
std::map::at
std::map::begin
std::map::cbegin
std::map::cend
std::map::clear
std::map::count
std::map::crbegin
std::map::crend
std::map::emplace
std::map::emplace_hint
std::map::empty
std::map::end
std::map::equal_range
std::map::erase
std::map::extract
std::map::find
std::map::get_allocator
std::map::insert
std::map::insert_or_assign
std::map::key_comp
std::map::lower_bound
std::map::map
std::map::max_size
std::map::merge
std::map::operator[]
std::map::rbegin
std::map::rend
std::map::size
std::map::swap
std::map::try_emplace
std::map::upper_bound
std::map::value_comp
std::map::value_compare
std::multimap
std::multimap::begin
std::multimap::cbegin
std::multimap::cend
std::multimap::clear
std::multimap::count
std::multimap::crbegin
std::multimap::crend
std::multimap::emplace
std::multimap::emplace_hint
std::multimap::empty
std::multimap::end
std::multimap::equal_range
std::multimap::erase
std::multimap::extract
std::multimap::find
std::multimap::get_allocator
std::multimap::insert
std::multimap::key_comp
std::multimap::lower_bound
std::multimap::max_size
std::multimap::merge
std::multimap::multimap
std::multimap::rbegin
std::multimap::rend
std::multimap::size
std::multimap::swap
std::multimap::upper_bound
std::multimap::value_comp
std::multimap::value_compare
std::multiset
std::multiset::begin
std::multiset::cbegin
std::multiset::cend
std::multiset::clear
std::multiset::count
std::multiset::crbegin
std::multiset::crend
std::multiset::emplace
std::multiset::emplace_hint
std::multiset::empty
std::multiset::end
std::multiset::equal_range
std::multiset::erase
std::multiset::extract
std::multiset::find
std::multiset::get_allocator
std::multiset::insert
std::multiset::key_comp
std::multiset::lower_bound
std::multiset::max_size
std::multiset::merge
std::multiset::multiset
std::multiset::rbegin
std::multiset::rend
std::multiset::size
std::multiset::swap
std::multiset::upper_bound
std::multiset::value_comp
std::priority_queue
std::priority_queue::emplace
std::priority_queue::empty
std::priority_queue::pop
std::priority_queue::priority_queue
std::priority_queue::push
std::priority_queue::size
std::priority_queue::swap
std::priority_queue::top
std::queue
std::queue::back
std::queue::emplace
std::queue::empty
std::queue::front
std::queue::pop
std::queue::push
std::queue::queue
std::queue::size
std::queue::swap
std::set
std::set::begin
std::set::cbegin
std::set::cend
std::set::clear
std::set::count
std::set::crbegin
std::set::crend
std::set::emplace
std::set::emplace_hint
std::set::empty
std::set::end
std::set::equal_range
std::set::erase
std::set::extract
std::set::find
std::set::get_allocator
std::set::insert
std::set::key_comp
std::set::lower_bound
std::set::max_size
std::set::merge
std::set::rbegin
std::set::rend
std::set::set
std::set::size
std::set::swap
std::set::upper_bound
std::set::value_comp
std::stack
std::stack::emplace
std::stack::empty
std::stack::pop
std::stack::push
std::stack::size
std::stack::stack
std::stack::swap
std::stack::top
std::swap(std::array)
std::swap(std::deque)
std::swap(std::forward_list)
std::swap(std::list)
std::swap(std::map)
std::swap(std::multimap)
std::swap(std::multiset)
std::swap(std::priority_queue)
std::swap(std::queue)
std::swap(std::set)
std::swap(std::stack)
std::swap(std::unordered_map)
std::swap(std::unordered_multimap)
std::swap(std::unordered_multiset)
std::swap(std::unordered_set)
std::swap(std::vector)
std::tuple_element<std::array>
std::tuple_size(std::array)
std::unordered_map
std::unordered_map::at
std::unordered_map::begin
std::unordered_map::begin(int)
std::unordered_map::bucket
std::unordered_map::bucket_count
std::unordered_map::bucket_size
std::unordered_map::cbegin
std::unordered_map::cbegin
std::unordered_map::cend
std::unordered_map::cend
std::unordered_map::clear
std::unordered_map::count
std::unordered_map::emplace
std::unordered_map::emplace_hint
std::unordered_map::empty
std::unordered_map::end
std::unordered_map::end(int)
std::unordered_map::equal_range
std::unordered_map::erase
std::unordered_map::extract
std::unordered_map::find
std::unordered_map::get_allocator
std::unordered_map::hash_function
std::unordered_map::insert
std::unordered_map::insert_or_assign
std::unordered_map::key_eq
std::unordered_map::load_factor
std::unordered_map::max_bucket_count
std::unordered_map::max_load_factor
std::unordered_map::max_size
std::unordered_map::merge
std::unordered_map::operator[]
std::unordered_map::rehash
std::unordered_map::reserve
std::unordered_map::size
std::unordered_map::swap
std::unordered_map::try_emplace
std::unordered_map::unordered_map
std::unordered_multimap
std::unordered_multimap::begin
std::unordered_multimap::begin(int)
std::unordered_multimap::bucket
std::unordered_multimap::bucket_count
std::unordered_multimap::bucket_size
std::unordered_multimap::cbegin
std::unordered_multimap::cbegin
std::unordered_multimap::cend
std::unordered_multimap::cend
std::unordered_multimap::clear
std::unordered_multimap::count
std::unordered_multimap::emplace
std::unordered_multimap::emplace_hint
std::unordered_multimap::empty
std::unordered_multimap::end
std::unordered_multimap::end(int)
std::unordered_multimap::equal_range
std::unordered_multimap::erase
std::unordered_multimap::extract
std::unordered_multimap::find
std::unordered_multimap::get_allocator
std::unordered_multimap::hash_function
std::unordered_multimap::insert
std::unordered_multimap::key_eq
std::unordered_multimap::load_factor
std::unordered_multimap::max_bucket_count
std::unordered_multimap::max_load_factor
std::unordered_multimap::max_size
std::unordered_multimap::merge
std::unordered_multimap::rehash
std::unordered_multimap::reserve
std::unordered_multimap::size
std::unordered_multimap::swap
std::unordered_multimap::unordered_multimap
std::unordered_multiset
std::unordered_multiset::begin
std::unordered_multiset::begin(int)
std::unordered_multiset::bucket
std::unordered_multiset::bucket_count
std::unordered_multiset::bucket_size
std::unordered_multiset::cbegin
std::unordered_multiset::cbegin
std::unordered_multiset::cend
std::unordered_multiset::cend
std::unordered_multiset::clear
std::unordered_multiset::count
std::unordered_multiset::emplace
std::unordered_multiset::emplace_hint
std::unordered_multiset::empty
std::unordered_multiset::end
std::unordered_multiset::end(int)
std::unordered_multiset::equal_range
std::unordered_multiset::erase
std::unordered_multiset::extract
std::unordered_multiset::find
std::unordered_multiset::get_allocator
std::unordered_multiset::hash_function
std::unordered_multiset::insert
std::unordered_multiset::key_eq
std::unordered_multiset::load_factor
std::unordered_multiset::max_bucket_count
std::unordered_multiset::max_load_factor
std::unordered_multiset::max_size
std::unordered_multiset::merge
std::unordered_multiset::rehash
std::unordered_multiset::reserve
std::unordered_multiset::size
std::unordered_multiset::swap
std::unordered_multiset::unordered_multiset
std::unordered_set
std::unordered_set::begin
std::unordered_set::begin(int)
std::unordered_set::bucket
std::unordered_set::bucket_count
std::unordered_set::bucket_size
std::unordered_set::cbegin
std::unordered_set::cbegin
std::unordered_set::cend
std::unordered_set::cend
std::unordered_set::clear
std::unordered_set::count
std::unordered_set::emplace
std::unordered_set::emplace_hint
std::unordered_set::end
std::unordered_set::end(int)
std::unordered_set::equal_range
std::unordered_set::erase
std::unordered_set::extract
std::unordered_set::find
std::unordered_set::get_allocator
std::unordered_set::hash_function
std::unordered_set::insert
std::unordered_set::key_eq
std::unordered_set::load_factor
std::unordered_set::max_bucket_count
std::unordered_set::max_load_factor
std::unordered_set::max_size
std::unordered_set::merge
std::unordered_set::rehash
std::unordered_set::reserve
std::unordered_set::size
std::unordered_set::swap
std::unordered_set::unordered_set
std::uses_allocator<std::priority_queue>
std::uses_allocator<std::queue>
std::uses_allocator<std::stack>
std::vector
std::vector::assign
std::vector::at
std::vector::back
std::vector::begin
std::vector::capacity
std::vector::cbegin
std::vector::cend
std::vector::clear
std::vector::crbegin
std::vector::crend
std::vector::data
std::vector::emplace
std::vector::emplace_back
std::vector::empty
std::vector::end
std::vector::erase
std::vector::front
std::vector::get_allocator
std::vector::insert
std::vector::max_size
std::vector::operator[]
std::vector::pop_back
std::vector::push_back
std::vector::rbegin
std::vector::rend
std::vector::reserve
std::vector::resize
std::vector::shrink_to_fit
std::vector::size
std::vector::swap
std::vector::vector
std::vector<bool>
std::vector<bool>::flip
std::vector<bool>::reference
std::vector<bool>::swap
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std::unordered_set::empty

STD：无序[医]

bool empty() const;​(since C++11)

检查容器是否没有元素，即是否begin() == end()...

参数

%280%29

返回值

true如果容器是空的，false否则。

例外

noexcept规格：

noexcept

复杂性

常量。

例

下面的代码使用empty以检查std::unordered_set<int>包含任何元素：

二次

#include <unordered_set>
#include <iostream>
 
int main()
{
    std::unordered_set<int> numbers;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
 
    numbers.insert(42
    numbers.insert(13317 
    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

二次

产出：

二次

Initially, numbers.empty(): 1
After adding elements, numbers.empty(): 0

二次

另见

sizereturns the number of elements (public member function)

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