如何在构造函数中初始化struct的动态数组？

Question

This is a Stack class based on a dynamic array of struct for Depth First Search (DFS). The program is not able to run whenever it encounters the function, push(), which shows that the array is not successfully initialized in the constructor.

I have tried to look for the error and even changing the dynamic array of struct into parallel arrays but it still does not work. I apologize if the problem seems to be too simple to be solved as I do not have a strong foundation in C++.

#include <iostream>
#include <iomanip>
#ifndef HEADER_H
#define HEADER_H

using namespace std;

struct Value
{
    int row;  // row number of position
    int col;  // column number of position

    //operator int() const { return row; }
};

class ArrayStack
{

public:
    int top;
    Value* array;
    ArrayStack();
    bool isEmpty();
    bool isFull();
    void push(int r, int c);
    void pop();
    int poprowvalue(int value);
    int popcolvalue(int value);
    int peekrow(int pos);
    int peekcol(int pos);
    int count();
    void change(int pos, int value1, int value2);
    void display();
    void resize();
private:
    int size;
};

ArrayStack::ArrayStack()
{
    //Initialize all variablies
    top = -1;
    size = 10;
    Value * array = new Value[size];
    for (int i = 0; i < size; i++)
    {
        array[i].row = 0;
        array[i].col = 0;
    }
}

bool ArrayStack::isEmpty()
{
    if (top == -1)
        return true;
    else
        return false;
}

bool ArrayStack::isFull()
{
    if (top == size - 1)
        return true;
    else
        return false;
}

void ArrayStack::resize()
{
    if (isFull())
        size *= 2;
    else if (top == size / 4)
        size /= 2;
}

void ArrayStack::push(int r, int c)
{
    if (isEmpty() == false)
        resize();
    array[top + 1].row = r;
    array[top + 1].col = c;
    top++;
}

void ArrayStack::pop()
{
    int value;

    if (isEmpty())
    {
        cout << "Stack underflow" << endl;
    }
    else
    {
        poprowvalue(array[top].row);
        popcolvalue(array[top].col);
        array[top].row = 0;
        array[top].col = 0;
        top--;
    }
}

int ArrayStack::poprowvalue(int v)
{
    return v;
}

int ArrayStack::popcolvalue(int v)
{
    return v;
}

int ArrayStack::peekrow(int pos)
{
    if (isEmpty())
        cout << "Stack underflow" << endl;
    else
        return array[pos].row;
}

int ArrayStack::peekcol(int pos)
{
    if (isEmpty())
        cout << "Stack underflow" << endl;
    else
        return array[pos].col;
}

int ArrayStack::count()
{
    return (top + 1);
}

void ArrayStack::change(int pos, int value1, int value2)
{
    if (isEmpty())
        cout << "Stack underflow" << endl;
    else
    {
        array[pos].row = value1;
        array[pos].col = value2;
    }

}

void ArrayStack::display()
{
    for (int i = size - 1; i > -1; i--)
    {
        cout << array[i].row << "  " << array[i].col << endl;
    }


}

#endif 

I expect it to run well but an exception is always thrown on line 80, which is as follows:

Exception thrown at 0x00007FF6A160487C in Assignment1.exe: 0xC0000005: Access violation writing location 0x0000000000000000.

Answer 1

The problem is this line right here:

Value * array = new Value[size];

This declares a new array variable. You are allocating that array instead, and not your member variable array .

The answer is simple, just change it to this instead:

array = new Value[size];