Error with Hash Table in c++

Question

I written a simple program for insert data in Hash Table and remove data from it with C++ language. My program error is: undefined reference to 'HashTable::insert(int&)' How to fix this error?

#include <iostream>
#include <list>
#include <vector>

using namespace std;

I Create a template for give all variables.

template <typename HashedObj>
class HashTable {
public:
    explicit HashTable(int cusize = 101) {}

    bool contains(const HashedObj& x) const
    {
        auto& whichList = theLists[myhash(x)];
        return find(begin(whichList), end(whichList), x) != end(whichList);
    }

    void makeEmpty()
    {
        for (auto& thisList : theLists)
            thisList.clear();
    }

    bool insert(const HashedObj& x)
    {
        auto& whichList = theLists[myhash(x)];
        if (find(begin(whichList), end(whichList), x) != end(whichList))
            return false;
        whichList.push_back(x);

        //Rehash
        if (++currentSize > theLists.size())
            rehash();

        return true;
    }

    bool insert(HashedObj& x);
    bool remove(const HashedObj& x)
    {
        auto& whichList = theLists[myhash(x)];
        auto itr = find(begin(whichList), end(whichList), x);

        if (itr == end(whichList))
            return false;

        whichList.erase(itr);
        --currentSize;
        return true;
    }


private:
    vector<list<HashedObj>> theLists; //The array of Lists
    int currentSize;

    void rehash();
    size_t myhash(const HashedObj& x) const
    {
        static hash<HashedObj> hf;
        return hf(x) % theLists.size();
    }
};

In the main function i create a HashTable with int variable for example and insert 10 number to it but compiler has a error on test = t.insert(i); for insert function.

int main()
{
    HashTable<int> t;

    bool test;
    for (int i = 0; i < 10; i++) {
        test = t.insert(i);
    }
}

tip: look at the paramenter of <br> bool insert(const HashedObj& x) — travisjayday
The easiest fix is to remove this declaration bool insert(HashedObj& x);. Alternatively, you may want to implement this overload. Finally, you can use t.insert(std::move(i)) instead of t.insert(i) (you probably don't want to do that with non-trivial types, though). The options are listed in the order of my preference. — Dietmar Kühl
Then you'll have a problem with rehash being declared but not defined. — Doug Coburn
Is the second version of insert defined in a separate source file? If so, what's its definition? If not, why have you declared it? — Sam Marinelli

Devin L. Devin L. · Accepted Answer · 2017-08-01T22:51:24

There seems to be two bool insert(params) functions in your code:

 bool insert(const HashedObj& x)
{
    auto& whichList = theLists[myhash(x)];
    if (find(begin(whichList), end(whichList), x) != end(whichList))
        return false;
    whichList.push_back(x);

    //Rehash
    if (++currentSize > theLists.size())
        rehash();

    return true;
}

and here:

bool insert(HashedObj& x);

Remove one of them.

Edit: As @DietmarKühl suggested, you should remove the second implementation.

Error with Hash Table in c++

2 Answers