begin and end
- C++ course
- Intermediate
- Lesson 60/116
- 5 min
Learn iterator ranges with begin() and end().
begin and end
Every STL container offers two member functions: begin() returns an iterator to the first element, and end() returns the position one past the last element (past-the-end). Together they define a range: [begin, end).
This range is half-open: begin is included, end is excluded. Loops use it != v.end(), not <. That is because every iterator category supports != but only random access iterators support <. So != is more portable.
Half-open range
The half-open nature of [begin, end) makes empty containers easy. For an empty vector begin() == end() and the loop runs zero times. No special empty check is needed.
end() is never dereferenced. The position it points at is not a valid element. It is used only for comparison. This design is consistent across all STL algorithms such as std::find and std::sort: they all expect a [begin, end) range. That is why this range idea is the foundation of the STL.
Practice Print with begin and end
Print the vector v = {5, 4, 3, 2, 1} in a while loop using v.begin() and v.end(). Add a space after each element.
Starter code
#include <iostream>
#include <vector>
int main() {
std::vector<int> v = {5, 4, 3, 2, 1};
// Print using begin and end
return 0;
}Sample solution
#include <iostream>
#include <vector>
int main() {
std::vector<int> v = {5, 4, 3, 2, 1};
auto it = v.begin();
while (it != v.end()) {
std::cout << *it << " ";
++it;
}
return 0;
}Expected output
5 4 3 2 1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the loop condition
auto it = v.begin();
while (it != v.____()) {
++it;
}auto it = v.begin();
while (it != v.end()) {
++it;
}Explanation: v.end() returns the position past the last element.
2 What does the v.end() iterator represent?
std::vector<int> v = {1, 2, 3};
auto e = v.end();- The first element
- The position past the last element Correct answer
- The last element
- An empty container
Explanation: end() is the position past the last and is never dereferenced.
3 Match each concept to its description
| Term | Meaning |
|---|---|
v.begin() |
Iterator to first |
v.end() |
Past the last |
[begin, end) |
Half-open range |
begin == end |
Empty container |