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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

Views

span (C++20)

 

std::unordered_set

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::empty

unordered_set::size

unordered_set::max_size

Modifiers

unordered_set::clear

unordered_set::insert

unordered_set::emplace

unordered_set::emplace_hint

unordered_set::erase

unordered_set::swap

unordered_set::extract (C++17)

unordered_set::merge (C++17)

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

erase_if (C++20)

Deduction guides(C++17)

 

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

end cend (C++11)	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)