I have a vector of pointer of a custom object std::vector<MyObject*>. The object has an index, a number and a timestamp (time of creation of the object). The timestamp is unique, the number can be either -1 (the object is not been assigned a number yet) or a positive value; if the object has a number greater than 0, the number is unique.

class MyObject {
private:
    int id;
    int number;
    time_t timestamp;
public:
    MyObject(int id, int number, time_t timestamp) : id(id), number(number), timestamp(timestamp) {}
};

I want to order the vector using a custom comparison function: if the two instances of my object have a number, I order using the number (descending), if not I order using the timestamp (descending).

So I added the following to the MyObject class:

    static bool compareByDescendingNumberAndTimestamp(MyObject * a, MyObject * b) {
        if (a->number > 0 && b->number > 0) {
            return a->number > b->number;
        }
        return a->timestamp > b->timestamp;
    }

And finally sort the vector:

std::vector<MyObject*> myObjects;
auto object1 = new MyObject(1, 24097, 1200);
auto object2 = new MyObject(2, 24096, 1100);
auto object3 = new MyObject(3, -1, 1000);
auto object4 = new MyObject(4, -1, 900);
auto object5 = new MyObject(5, 24099, 800);
auto object6 = new MyObject(6, 24095, 850);
myObjects.push_back(object1);
myObjects.push_back(object2);
myObjects.push_back(object3);
myObjects.push_back(object4);
myObjects.push_back(object5);
myObjects.push_back(object6);
std::sort(myObjects.begin(), myObjects.end(), MyObject::compareByDescendingNumberAndTimestamp);

The order I intended to have is the following:

ID   Number  Timestamp
5    24099    800
1    24097   1200
2    24096   1100
3    -       1000
4    -        900
6    24095    850

But what I actually got is:

ID   Number  Timestamp
1    24097   1200
2    24096   1100
3    -       1000
4    -        900
5    24099    800
6    24095    850

After some research I find this page. As far as I understood, my comparison function does not satisfy the requirements of Compare. In particular the comp(a, b) does not establish a strict weak ordering relation.

Is there a way I can write a comparison function to order my vector as I want?

Note: I’ve been using c++17.