实现动态数组数据结构时出现"double free or corruption"错误

我正在尝试为我的数据结构和算法课程实现动态数组数据结构，但我认为我在内存管理方面遇到了一些麻烦。我的模板类如下。

ArrayList.h

#include <iostream>
#include <cstring>
using namespace std;
#define Length(array) (sizeof((array))/sizeof((array[0])))
template <class T>
class ArrayList
{
    public:
    ArrayList() {a = new T[1]; n = 0;}
    ~ArrayList() {delete [] a;}
    int size();
    int backingSize();
    T get(int i);
    T set(int i, T x);
    void add(int i, T x);
    T remove (int i);
    private:
    void resize();
    T *a;
    int n;
};
template <class T>
int ArrayList<T>::size() { return n; }
template <class T>
int ArrayList<T>::backingSize() { return Length(a); }
template <class T>
T ArrayList<T>::get(int i) { return a[i]; }
template <class T>
T ArrayList<T>::set(int i, T x) 
{ 
    T temp = a[i];
    a[i] = x;
    return temp;
}
template <class T>
void ArrayList<T>::add(int i, T x) 
{
    if (n+1 > Length(a)) resize();
    for (int j = n; j > i; j--) a[j] = a[j-1];
    a[i] = x;
    n++;
}
template <class T>
T ArrayList<T>::remove(int i) 
{
    T temp = a[i];
    for (int j = i; j < n-1; j++) a[j] = a[j+1];
    n--; 
    if (Length(a) > 3*n) resize();
    return temp; 
}
template <class T>
void ArrayList<T>::resize() 
{
    if ( n+1 > Length(a))
    {
        cout << "Making Biggern"; 
        T* tempArr = new T[2*n];
        memcpy(tempArr, a, n * sizeof(T));
        delete [] a;
        a = tempArr;
    }
    else   //  (Length(a) > 3*n)
    {
        cout << "Making Smallern";
        T* tempArr = new T[n/2];
        memcpy(tempArr, a, n * sizeof(T));
        delete [] a;
        a = tempArr;
    }
}

然后我使用以下主要函数对其进行测试

TestArrayList.cpp

#include "ArrayList.h"
#include <iostream>
using namespace std;
int main()
{
    ArrayList <int> myList;
    cout << myList.size() << "nn";
    myList.add(0,15);
    cout << myList.get(0) << ", " << myList.size() << ", " << myList.backingSize() << "n";
    myList.add(1,34);
    cout << myList.get(1) << ", " << myList.size() << ", " << myList.backingSize() << "n";
    myList.add(2,23);
    cout << myList.get(2) << ", " << myList.size() << ", " << myList.backingSize() << "n";
    myList.add(3,1);
    cout << myList.get(3) << ", " << myList.size() << ", " << myList.backingSize() << "nn";
    myList.~ArrayList();
}

代码编译并运行，并输出到终端：

15, 1, 2
34, 2, 2
Making Bigger
23, 3, 2
Making Bigger
1, 4, 2
*** Error in `./TestArrayList': double free or corruption (fasttop): 0x000000000090c010 ***
Aborted

它似乎按预期工作，get 函数在其索引处返回正确的值，size 函数返回数组的正确长度，并且没有 seg 错误。但是，backingSize()函数总是返回 2，并且我认为最后抛出的错误与糟糕的内存管理有关。我已经难倒了一段时间，所以任何帮助将不胜感激。