From cppreference.com
iteratorbegin()noexcept; (1) (since C++11)const_iteratorbegin()constnoexcept; (2) (since C++11)const_iteratorcbegin()constnoexcept; (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
.
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>structPoint{doublex,y;};intmain(){Pointpts[3]={{1,0},{2,0},{3,0}};// points is a set containing the addresses of pointsstd::unordered_set<Point*>points={pts,pts+1,pts+2};// Change each y-coordinate of (i, 0) from 0 into i^2 and print the pointfor(autoiter=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 10for(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
returns an iterator to the end
(public member function)
(C++11)(C++14)
returns an iterator to the beginning of a container or array
(function template)