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

Since C++11

Returns an iterator to the first element of the unordered_set.

# Declarations

iterator begin() noexcept;

(since C++11)

const_iterator begin() const noexcept;

(since C++11)

const_iterator cbegin() const noexcept;

(since C++11)

# Return value

Iterator to the first element.

# 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

#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 << ") ";
    }
}

# See also