std::sort
- C++ course
- Intermediate
- Lesson 70/116
- 5 min
Learn to sort with std::sort.
std::sort
std::sort sorts a range in place. It takes two iterators: std::sort(v.begin(), v.end()). By default it sorts in ascending order (small to large). It is defined in <algorithm>.
Sorting requires random access iterators; that is why it works on std::vector and std::array but not on std::list. The sort is efficient (usually O(n log n)). It modifies the container directly and does not create a new one. That is why it is called an 'in-place' sort.
Descending sort
To sort descending, pass std::greater<int>() as the third parameter: std::sort(v.begin(), v.end(), std::greater<int>());. This uses the > operator to sort large to small.
std::greater is a functor defined in <functional>. A functor is a class with operator(); it can be called like a function. At an advanced level you can write your own functors or use lambdas, but ready-made functors like std::greater cover most cases.
Practice Sort and print a vector
Sort the vector v = {5, 2, 8, 1, 9} in ascending order with std::sort. Then print each element followed by a space in a for loop.
Starter code
#include <iostream>
#include <vector>
#include <algorithm>
int main() {
std::vector<int> v = {5, 2, 8, 1, 9};
// Sort with std::sort, print with a for loop
return 0;
}Sample solution
#include <iostream>
#include <vector>
#include <algorithm>
int main() {
std::vector<int> v = {5, 2, 8, 1, 9};
std::sort(v.begin(), v.end());
for (int x : v) {
std::cout << x << " ";
}
return 0;
}Expected output
1 2 5 8 9
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How does std::sort order by default?
std::sort(v.begin(), v.end());- Descending (large to small)
- Randomly
- Reversed
- Ascending (small to large) Correct answer
Explanation: The default is ascending order.
2 Complete the sort call
std::____(v.begin(), v.end());std::sort(v.begin(), v.end());Explanation: std::sort sorts the range.
3 Match each piece to its role
| Term | Meaning |
|---|---|
std::sort(begin, end) |
Ascending sort |
std::greater<int>() |
Descending sort |
v.begin() |
Range start |
v.end() |
Range end |