< operator overloading for struct member in linked list C++

Question

So basicaly I have my struct that keeps data before assigning it to value of linked list and helps me to retrieve it later

struct Student
{

private:

    string surname ;
    string names ;
    int index;
    float mark;
}

and here is my implementation of inserting into sorted linked list

template<typename T>
void List<T>::insert(T v)
{
    Node* pred = nullptr;
    Node* succ = head;

    while(succ != nullptr && succ->value < v) <- here
    {
        pred = succ;
        succ = succ->next;
    }
...

my problem is i need to sort it by index and none of my implementations of < operator overloading seems to work

bool operator<(const Student&){
    return  next->index < this->index;}

I was doing some overloading on operators like == or + but never <, can anyone give me advice how it should look?

Can you [edit] your question, and replace all isolated code snippets with a single, complete [mre] that everyone else can cut/paste ***exactly as shown*** into an empty file, then compile, run, and reproduce your problem? What does "none of my implementations ... seems to work" mean? — Sam Varshavchik, Sep 09 '21 at 00:43
`operator<` should take two `Student` objects (by reference) and return `true` if the first is less than the second. Just write that function. — Pete Becker, Sep 09 '21 at 00:59
Handy reading on operators across the board: [What are the basic rules and idioms for operator overloading?](https://stackoverflow.com/questions/4421706/what-are-the-basic-rules-and-idioms-for-operator-overloading) — user4581301, Sep 09 '21 at 01:05
Could you add an explanation of how/why you believe your `operator<` should work? It might help to work from an example, say start with `Student a; Student b;`, add suitable initializations, then walk through the evaluation of the expression `a < b`, a.k.a. `a.operator<(b)`. (Forcing yourself to explain your reasoning to others is an effective debugging technique sometimes called [rubber duck debugging](https://en.wikipedia.org/wiki/Rubber_duck_debugging).) — JaMiT, Sep 09 '21 at 01:35
For a problem description as detailed as *"none [...] seems to work"*, the answer "because they had bugs" seems to be at about the same level of helpfulness. What led you to the conclusion that the version of `operator<` in your question does not work? Error while compiling? (Copy-paste the error message.) Strange order while running? (Give a specific example with the actual and expected result.) One of those weird "undefined behavior" outcomes like formatting your hard drive? — JaMiT, Sep 09 '21 at 04:10

score 0 · Answer 1 · answered Sep 09 '21 at 02:43

index is private, meaning you need to either make it a member function or declare it as a friend.

struct Student {

    bool operator<(const Student& other) const {
        return index < other.index;
    }

private:
    string surname;
    string names;
    int index;
    float mark;
};

You can specify this->index instead of just index, but most of the time that isn't necessary.

Also, as a side note, if you're using C++ 20, I recommend overloading the spaceship operator instead, as that will automatically generate appropriate definitions for all the comparison operators (except == and !=):

    auto operator<=>(const Student& other) {
        return index <=> other.index;
    }

*"you need to either make it a member function or [...]"* -- given that the question's version shows only one parameter for this *binary* operator, I would guess that it already is a member function. Similar setup to how you presented `operator<=>`, no? (Of course, if you don't like guessing, you could ask for clarification before answering.) — JaMiT, Sep 09 '21 at 04:03

< operator overloading for struct member in linked list C++

1 Answers1