CODEWITHSUNDEEP
c++
Eric Goncalves
Eric Goncalves

Reputation: 5353

Recreating vector with template class c++

I am attempting to recreate vectors using my own class called MyVector.

template<class T>
class MyVector{
    private:
        T *v;
        int size;
        int max;

    public:
        MyVector();
        MyVector(int n);
        MyVector(int n, int k);
        MyVector(const MyVector &l);
        void grow();
        MyVector<T>& operator=(const MyVector &lhs);
        T &operator[](unsigned int i);
        void push_back(T t);
        int capacity();
        int length();
        void reserve (int n);
        void resize(int);
};

i am attemping to recreate the push_back() function that vector has. I understand I need to create a copy of the original array with a size of size+1. but when I try:

template<class T>
void MyVector<T>::push_back(T t) {
    MyVector<T> *temp = v;

}

I get the error:

main.cpp: In member function âvoid MyVector<T>::push_back(T) [with T = int]â:
main.cpp:34:   instantiated from here
main.cpp:117: error: cannot convert âint*â to âMyVector<int>*â in initialization

I am fairly new to c++, any help is appreciated. thanks!

EDIT My new push_back class

template<class T>
void MyVector<T>::push_back(T t) {
    T *temp = v;
    v = new T[++size];
    temp[size] = t;

    for (int i = 0; i < size + 1; ++i){
        v[i] = temp[i];
    }

    delete [] temp;
}

When I call and print the vector in my main program it just appends a 0 to the end of the vector.

Upvotes: 0

Views: 1705

Answers (2)

Cheers and hth. - Alf
Cheers and hth. - Alf

Reputation: 145239

In MyVector<T> *temp = v; with T = int, the v refers to the data member that has type int*. You're trying to use that as an initializer for a MyVector*. Those are pointers to different types, incompatible pointers.

By the way, don't just increase the buffer by 1.

Double its size, or increase by a constant factor, so as to avoid quadratic behavior.

std::vector guarantees amortized linear time for push_back.

Upvotes: 4

Moha Dehghan
Moha Dehghan

Reputation: 18443

You are assigning a field of type T* to a variable of type MyVector<T>*. That's why you are getting the error. Change the line to:

T *temp = v;

Upvotes: 1

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