| iterator begin(); |
|
(since C++11) |
| const_iterator begin() const; |
|
(since C++11) |
| const_iterator cbegin() const; |
|
(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().
Parameters
(none)
Return value
Iterator to the first element
Exceptions
Complexity
Constant
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 << ") ";
}
}Possible output:
(3, 9) (1, 1) (2, 4)
(3, 19) (1, 11) (2, 14)
See also
|
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returns an iterator to the end
(public member function) |