std::unordered_set<Key,Hash,KeyEqual,Allocator>::begin, std::unordered_set<Key,Hash,KeyEqual,Allocator>::cbegin

 

C++

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list

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Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

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stack

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flat_set (C++23)

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std::unordered_set

Member types
Member functions
unordered_set::unordered_set unordered_set::~unordered_set unordered_set::operator= unordered_set::get_allocator Iterators unordered_set::beginunordered_set::cbegin unordered_set::endunordered_set::cend Capacity unordered_set::size unordered_set::max_size unordered_set::empty Modifiers unordered_set::clear unordered_set::erase unordered_set::swap unordered_set::extract (C++17) unordered_set::merge (C++17) unordered_set::insert unordered_set::insert_range (C++23)   unordered_set::emplace unordered_set::emplace_hint	Lookup unordered_set::count unordered_set::find unordered_set::contains (C++20) unordered_set::equal_range Bucket interface unordered_set::begin(size_type)unordered_set::cbegin(size_type) unordered_set::end(size_type)unordered_set::cend(size_type) unordered_set::bucket_count unordered_set::max_bucket_count unordered_set::bucket_size unordered_set::bucket Hash policy unordered_set::load_factor unordered_set::max_load_factor unordered_set::rehash unordered_set::reserve Observers unordered_set::hash_function unordered_set::key_eq
Non-member functions
operator==operator!= (until C++20)	std::swap(std::unordered_set) erase_if(std::unordered_set) (C++20)
Deduction guides (C++17)

 

iterator begin() noexcept;	(1)	(since C++11)
const_iterator begin() const noexcept;	(2)	(since C++11)
const_iterator cbegin() const noexcept;	(3)	(since C++11)

Returns an iterator to the first element of the unordered_set.

If the unordered_set is empty, the returned iterator will be equal to end().

Parameters

(none)

Return value

Iterator to the first element.

Complexity

Constant.

Notes

Because both iterator and const_iterator are constant iterators (and may in fact be the same type), it is not possible to mutate the elements of the container through an iterator returned by any of these member functions.

Example

Run this code

#include <iostream>
#include <unordered_set>
 
struct Point { double x, y; };
 
int main()
{
    Point pts[3] = {{1, 0}, {2, 0}, {3, 0}};
 
    // points is a set containing the addresses of points
    std::unordered_set<Point*> points = { pts, pts + 1, pts + 2 };
 
    // Change each y-coordinate of (i, 0) from 0 into i^2 and print the point
    for (auto iter = points.begin(); iter != points.end(); ++iter)
    {
        (*iter)->y = ((*iter)->x) * ((*iter)->x); // iter is a pointer-to-Point*
        std::cout << "(" << (*iter)->x << ", " << (*iter)->y << ") ";
    }
    std::cout << '\n';
 
    // Now using the range-based for loop, we increase each y-coordinate by 10
    for (Point* i : points)
    {
        i->y += 10;
        std::cout << "(" << i->x << ", " << i->y << ") ";
    }
}

Possible output:

(3, 9) (1, 1) (2, 4) 
(3, 19) (1, 11) (2, 14)

See also

endcend	returns an iterator to the end (public member function)
begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template)