visual-c++ - C/C++：“试图读取或写入受保护的内存”异常

Question

我的代码编译但抛出以下异常：

An unhandled exception of type 'System, Access Violation Exception' occured Additional Information: Attempted to read or write protected memory. . .

该错误与s=s+a[z][r]*b[f][h]

这里是代码的副本：

#include"stdafx.h"
#include"iostream"
using namespace std;
int main()
{
    int **a, **b;
    int z, r, f, h, a_r, a_c, b_r, b_c, s = 0;

    cout << "Enter the size of the matrix(nxm) :" << endl;
    cin >> a_r >> a_c;

    cout << "enter the size of the mask :" << endl;
    cin >> b_r >> b_c;

    a = (int **) malloc(10 * a_r);
    for (int i = 0; i < a_c; i++)
    {
        a[i] = (int *) malloc(10 * a_c);
    }

    b = (int **) malloc(10 * b_r);
    for (int i = 0; i < b_c; i++)
    {
        b[i] = (int *) malloc(10 * b_c);
    }

    for (int i = 0; i < a_r; i++)
    {
        for (int j = 0; j < a_c; j++)
        {
            a[i][j] = i + j;
        }
    }

    for (int i = 0; i < b_r; i++)
    {
        for (int j = 0; j < b_c; j++)
        {
            b[i][j] = i + j;
        }
    }

    int k = 1, d = 1;
    for (int i = 0; i < a_r; i++)
    {
        for (int j = 0; j < a_c; j++)
        {
            for (int n = -1; n <= 1; n++)
            {
                for (int e = -1; e <= 1; e++)
                {
                    z = i + n;
                    r = j + e;
                    f = k + n;
                    h = d + e;
                    if (z < 0 || z > a_r || r < 0 || r > a_c)
                    {
                        s = s + 0;
                    } else {
                        s = s + a[z][r] * b[f][h]; // runtime error occurs here
                    }
                }
            }
            a[i][j] = s;
            s = 0;
        }
    }
    return 0;
}

Answer 1

Here is one problem:

                if (z < 0 || z > a_r || r < 0 || r > a_c)

This should read:

                if (z < 0 || z >= a_r || r < 0 || r >= a_c)

Otherwise you're potentially accessing out-of-bounds elements.