cppType errorMedium

Custom comparator missing const qualifier

Time: 0:00

BugFind the bug and fix the code

What it should do

Insert item into std::set and return set count. Example: insertCustomTypeInSet(10) -> 1

What happens instead

Compiler error: passing 'const Item' as 'this' argument discards qualifiers in operator<

#include <iostream>
#include <set>

struct Item {
    int id;
    // Missing const qualifier on operator<
    bool operator<(const Item& other) {
        return id < other.id;
    }
};

int insertCustomTypeInSet(int id) {
    std::set<Item> items;
    items.insert(Item{id});
    return items.size();
}

int main() {
    std::cout << insertCustomTypeInSet(10) << std::endl;
    return 0;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the type errors pattern

Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.

Learn the type errors pattern Step through your own code

<iframe src="https://trybughunt.com/embed/2f73047c-ef25-4402-90e6-d83587a5cf75" title="Debugging challenge: Custom comparator missing const qualifier" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/2f73047c-ef25-4402-90e6-d83587a5cf75">TryBugHunt</a></p>

#include <iostream> #include <set> struct Item { int id; // Missing const qualifier on operator< bool operator<(const Item& other) { return id < other.id; } }; int insertCustomTypeInSet(int id) { std::set<Item> items; items.insert(Item{id}); return items.size(); } int main() { std::cout << insertCustomTypeInSet(10) << std::endl; return 0; }

Custom comparator missing const qualifier

What it should do

What happens instead

More type errors to practise

Custom comparator missing const qualifier

What it should do

What happens instead

More type errors to practise