std::unordered_set<Key,Hash,KeyEqual,Allocator>::begin, (3) - Linux Man Pages

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

NAME

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

Synopsis


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 container.


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


range-begin-end.svg

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 };


  //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  returns an iterator to the end
cend (public member function)