Sorting elements in struct in C++

Question

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

using namespace std;

struct properties{
    int index;    // student's index number
    string name;  // name of student
    int points;   // points of exam

    bool sorter(properties a, properties b){
        return a.points < b.points;
    }

};

int main()
{
    properties students[6];

    vector<int> v;

    for(int i = 0; i < 6; i++){
        cin >> students[i].index >> students[i].name >> students[i].points;
    }

    for(int i = 0; i < 6; i++){
        v.push_back(students[i].points);
    }

    stable_sort(students.begin(), students.end(), sorter);

    return 0;
}

I have the following program and now I have to expand it to print the elements in sorted order from highest points to lowest. I need the smallest and most simple code because time isn't an issue in my case. Any help is appreciated.

UPDATE: I am getting two errors:

error: expected primary-expression before ',' token
error: expected primary-expression before '+' token

On this line:

sort(properties, properties + 5);

have you tried [`std::sort`](http://en.cppreference.com/w/cpp/algorithm/sort)? — Erbureth, Dec 25 '13 at 12:54
@Erbureth Yes... but I don't know how to implement it with struct... I've used it before for arrays and it works perfectly, but I can't get it to work in this case.. — user2943407, Dec 25 '13 at 12:55
See the second form of `std::sort`, it allows you to specify your own comparator function. The documentation linked includes the example implementation. — Erbureth, Dec 25 '13 at 12:56
You have an array, so what is the problem? Sort it, as explained in the duplicate. — juanchopanza, Dec 25 '13 at 12:59
`sort(students.points, students.points+5, properties);` I have this and I get 3 errors. What am I doing wrong? — user2943407, Dec 25 '13 at 12:59
Well, I declared a bool function and I am still getting errors. — user2943407, Dec 25 '13 at 13:05

yakov · Accepted Answer · 2013-12-25T13:59:39.210

1

I'll just give you some consecutive tips:

Create std::vector and push you data into:
```
vector<properties> students;
```

Write the function which compares two structures and returns the comparison result. Don't make it a member of your structure. Notice that I've renamed it:

bool less_than(properties const& first, properties const& second) 
//my fault. Compiler is trying to call std::less<>() function instead of your.
{  
  return first.points < second.points;    
}

Call the std::sort function:

sort(students.begin(), students.end(), less_than);

The data in your students structure will be sorted in the descending order.

This code works: http://ideone.com/iMWcfi

edited Dec 25 '13 at 13:59

answered Dec 25 '13 at 13:25

yakov

444
3
14

Thanks, I'll try right now. One more question. Will the other properties of the student be in same order? Like the name of the student who when sorted goes first stays the same? – user2943407 Dec 25 '13 at 13:27
@user2943407 see [`std::stable_sort`](http://en.cppreference.com/w/cpp/algorithm/stable_sort) – Erbureth Dec 25 '13 at 13:28
@Erbureth so It's the same with sort() except different name, however I have a question. When I use stable_sort() in main(), it says that less is not declared and 'request for member 'begin' and 'end' in 'students' is non-class type 'properties[6]'. When I declare the sorting inside the struct, then it says students was not declared. What am I doing wrong?? – user2943407 Dec 25 '13 at 13:33
@user2943407 Keep updating the code in the question, so we can see what are you trying. – Erbureth Dec 25 '13 at 13:37
1

@user2943407 declare the `sorter` as `static` (`static bool sorter(...){...}`) and call it like `sort(students, students + 6, properties::sorter);` – Erbureth Dec 25 '13 at 13:44
@Erbureth Thanks a lot. I appreciate your help, you helped a LOT! Merry Christmas and happy holidays! – user2943407 Dec 25 '13 at 13:49

score 0 · Answer 2 · edited May 23 '17 at 11:56

0

See e.g. https://stackoverflow.com/a/10308722/1467943

bool operator <(const properties &a, const properties &b) {
  return a.points < b.points;
}

edited May 23 '17 at 11:56

Community

1
1

answered Dec 25 '13 at 13:24

ales_t

1,967
11
10

Sorting elements in struct in C++

2 Answers2