How to fix 'no overloaded function takes 2 arguments' error C++

Question

I'm trying to create a class for a hash table to contain unique pointers, but whenever I try to add a pointer to the table I get an error which points to a different file from a library I am using.

I've tried using .insert() instead of .emplace(). I've tried passing in a pair of the key and the pointer.

Both of these have resulted in a different error to the original

here is the Hash_Table class:

///<summary>
/// A struct for a hash table
///</summary>
template <typename T>
struct Hash_Table
{
public:
    ///<summary>
    /// Add an item to the hash table & return the item key
    ///</summary>
    int addItem(T newItem) {
        // Make the item into a unique pointer
        std::unique_ptr<T> itemPtr = std::make_unique<T>(newItem);

        //std::pair<int, std::unique_ptr<T>> pair = std::make_pair(tailPointer, itemPtr);

        while (!Table.emplace(tailPointer, itemPtr).second) {
            tailPointer++;
            //pair.first++;
        }

        tailPointer++;

        return tailPointer--;
    };

private:

    ///<summary>
    /// The actual hash table
    ///</summary>
    std::unordered_map<int, std::unique_ptr<T>> Table;

    ///<summary>
    /// Points to the key of the last item added to the hash table
    ///</summary>
    int tailPointer;
};

The issue happens in addItem() function when I try to table.emplace().

Error in file xmemory for code as shown above:

C2661: 'std::pair::pair': no overloaded function takes 2 arguments

Error in file HashTable.h for when using table.insert():

C2664: 'std::_List_iterator>> std::_Hash>,std::_Uhash_compare<_Kty,_Hasher,_Keyeq>,_Alloc,false>>::insert(std::_List_const_iterator>>,const std::pair>> &)': cannot convert argument 1 from 'int' to 'std::_List_const_iterator>>'

Error in file utility for when using table.insert or table.emplace(std::make_pair(tailPointer, itemPtr)):

C2440: '': cannot convert from 'initializer list' to '_MyPair'

`Table.emplace(tailPointer, itemPtr)` -> `Table.try_emplace(tailPointer, std::move(itemPtr))` (but C++17). — Jarod42, Sep 09 '19 at 09:18
`tailPointer++;` followed by `return tailPointer--;` is confusing me a bit... — CharonX, Sep 09 '19 at 09:21
Possible duplicate of [How do I pass a unique\_ptr argument to a constructor or a function?](https://stackoverflow.com/questions/8114276/how-do-i-pass-a-unique-ptr-argument-to-a-constructor-or-a-function) — Indiana Kernick, Sep 09 '19 at 09:24

score 1 · Answer 1 · answered Sep 09 '19 at 12:50

Multiple ways to fix your issue:

Solution 1:

int addItem(T newItem) {
    // Make the item into a unique pointer
    std::unique_ptr<T> itemPtr = std::make_unique<T>(newItem);

    // Unique_ptr doesn't have assignment operator instead it has move-assignment.
    // So it need to be moved only
    std::pair<int, std::unique_ptr<T>> pair = std::make_pair(tailPointer++, std::move(itemPtr));

    // For same above reason, it must be moved
    Table.insert(std::move(pair));

    return tailPointer;
};

Solution 2:

int addItem(T newItem) {
    Table.insert(std::make_pair(tailPointer++, std::make_unique<T>(newItem)));
    return tailPointer;
}

Solution 3:

int addItem(T newItem) {
    Table[tailPointer++] = std::make_unique<T>(newItem);
    return tailPointer;
}

Non of the above solutions will require C++ 17. All are from C++11. You should understand why you are getting the compilation error. With your existing code you are trying to assign or copy the unique_ptr which is not allowed. It can only be moved. This is what your compiler is trying to tell you.

v78 · Answer 2 · 2019-09-09T09:25:54.370

0

Using this, will resolve the unique_ptr problems, in c++11

int addItem(T newItem) {    
    // Make the item into a unique pointer
    while (!Table.emplace_hint(tailPointer, newItem).second) {
        tailPointer++;
        //pair.first++;
    }
    tailPointer++;
    return tailPointer--;
};

edited Sep 09 '19 at 09:25

answered Sep 09 '19 at 09:19

v78

2,803
21
44

score 0 · Answer 3 · answered Sep 09 '19 at 09:24

0

Thank you Jarod42, your fix did work.

The fix: Table.emplace(tailPointer, itemPtr) -> Table.try_emplace(tailPointer, std::move(itemPtr)) (but C++17). - Jarod42

answered Sep 09 '19 at 09:24

Falcon Oscuro

13
2
6

How to fix 'no overloaded function takes 2 arguments' error C++

3 Answers3