C++：分段错误（核心转储）

Question

I am trying to make a dynamic array implementation in C++ using pointers and templates so that I can accept all types. The code worked fine with int but using string gives an error. I tried online other SO questions but found nothing about my scenario.

Code:

#include <iostream>
#include <string>
using namespace std;

template <typename T>
class dynamicIntArray
{
private:
    T *arrPtr = new T[4]();
    int filledIndex = -1;
    int capacityIndex = 4;

public:
    // Get the size of array
    int size(void);

    // Insert a data to array
    bool insert(T n);

    // Show the array
    bool show(void);
};

template <typename T> 
int dynamicIntArray<T>::size(void)
{
    return capacityIndex + 1;
}

template <typename T> 
bool dynamicIntArray<T>::insert(T n)
{
    if (filledIndex < capacityIndex)
    {
        arrPtr[++filledIndex] = n;
        return true;
    }
    else if (filledIndex == capacityIndex)
    {
        // Create new array of double size
        capacityIndex *= 2;
        T *newarrPtr = new T[capacityIndex]();

        // Copy old array
        for (int i = 0; i < capacityIndex; i++)
        {
            newarrPtr[i] = arrPtr[i];
        }

        // Add new data
        newarrPtr[++filledIndex] = n;
        arrPtr = newarrPtr;

        return true;
    }
    else
    {
        cout << "ERROR";
    }
    return false;
}

template <typename T> 
bool dynamicIntArray<T>::show(void)
{
    cout << "Array elements are: ";
    for (int i = 0; i <= filledIndex; i++)
    {
        cout << arrPtr[i] << " ";
    }
    cout << endl;

    return true;
}

int main()
{
    dynamicIntArray<string> myarray;

    myarray.insert("A");
    myarray.insert("Z");
    myarray.insert("F");
    myarray.insert("B");
    myarray.insert("K");
    myarray.insert("C");

    cout << "Size of my array is: " << myarray.size() << endl;

    myarray.show();
}

Error:

segmentaion fault (core dumped)

Answer 1

Classic Off-by-one error :

if (filledIndex < capacityIndex)
{
    arrPtr[++filledIndex] = n;

Before you insert your 5th item filledIndex is 3 < 4 ( capacityIndex ). This leads to arrPtr[4] to be accessed (out of bound access as its range is currently [0..3]).

Fix it by initially setting filledIndex to 0 and change arrPtr[++filledIndex] = n; to arrPtr[filledIndex++] = n;

You should note that your code suffers from serious defects though: leaking memory, questionable names and style, etc. You might want to post its fixed version to https://codereview.stackexchange.com/ .