CppHow-ToBeginner · 3 min read

How to Sort Vector in C++: Syntax and Examples

To sort a std::vector in C++, use the std::sort function from the <algorithm> header. Call std::sort with the vector's begin() and end() iterators to sort elements in ascending order.

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Syntax

The basic syntax to sort a vector v is:

std::sort(v.begin(), v.end()); sorts in ascending order.
You can provide a custom comparison function for other orders.

Explanation:

std::sort: Function that sorts elements.
v.begin(): Iterator to the first element.
v.end(): Iterator just past the last element.

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std::sort(v.begin(), v.end());

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Example

This example shows how to sort a vector of integers in ascending order and print the result.

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#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> v = {5, 2, 9, 1, 5, 6};
    std::sort(v.begin(), v.end());

    for (int num : v) {
        std::cout << num << " ";
    }
    std::cout << std::endl;
    return 0;
}

Output

1 2 5 5 6 9

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Common Pitfalls

Common mistakes when sorting vectors include:

Not including the <algorithm> header, which causes compilation errors.
Passing the vector itself instead of iterators to std::sort.
Trying to sort vectors of non-comparable types without a custom comparator.

Wrong:

std::sort(v); // Error: expects iterators, not vector

Right:

std::sort(v.begin(), v.end());

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/* Wrong way - causes compilation error */
// std::sort(v); // Uncommenting this line will cause error

/* Right way */
std::sort(v.begin(), v.end());

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Quick Reference

Operation	Code Example	Description
Sort ascending	std::sort(v.begin(), v.end());	Sorts vector elements from smallest to largest
Sort descending	std::sort(v.begin(), v.end(), std::greater<>());	Sorts vector elements from largest to smallest
Custom sort	std::sort(v.begin(), v.end(), [](int a, int b){ return a % 10 < b % 10; });	Sorts by last digit using a lambda function

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Key Takeaways

Use std::sort with vector's begin() and end() iterators to sort elements.

Include header to access std::sort function.

Pass a custom comparator to std::sort for descending or custom order.

Do not pass the vector itself to std::sort; always use iterators.

Sorting works only if elements are comparable or a comparator is provided.