c++20 Sorting Vector of structs with structs member variable and std::ranges

Question

I have a simple struct

struct MyStruct
{
    int x;
}

I have a vector of MyStructs.

vector<MyStruct> myStructs;
int n = 10;

for(auto i = 0; i < n; i++)
    myStructs.push_back(MyStruct{.x = n - i});

How will I sort myStructs according to member variable .x using std::ranges?

This page has great example at bottom, how we can use [`std::ranges`](https://en.cppreference.com/w/cpp/algorithm/ranges/sort) — pvc, Feb 27 '21 at 12:28

score 4 · Accepted Answer · answered Feb 27 '21 at 13:59

4

using projection:

std::ranges::sort(myStructs, {}, &MyStruct::x); //< sort by x

answered Feb 27 '21 at 13:59

康桓瑋

Do you know the reason why i am getting ` error: 'sort' is not a member of 'std::ranges'; did you mean 'std::sort'?`? – Inyoung Kim 김인영 Feb 27 '21 at 22:32
@InyoungKim김인영 It might be the case that your compiler doesn't fully support `ranges` yet. – L. F. Feb 28 '21 at 03:40
@InyoungKim김인영 Or that you forgot to `#include ` – Ted Lyngmo Feb 28 '21 at 10:25

score 1 · Answer 2 · answered Feb 27 '21 at 12:27

1

Since you haven't provided a member operator< (or operator<=>) you can do it using a lambda:

#include <algorithm>

std::ranges::sort(myStructs, [](auto& lhs, auto& rhs) { return lhs.x < rhs.x; });

answered Feb 27 '21 at 12:27

Ted Lyngmo

2 Answers2