Access Violation Exception Raised when Accessing a Dynamic 2D char Array - c++

Question

I have currently a problem with the following C++ class, which holds the model logic of a cube. The constructor creates a dynamic 2d char array with the following content:
[ [0,0,0,0,0,0],
[1,1,1,1,1,1],
[2,2,2,2,2,2],
[3,3,3,3,3,3],
[4,4,4,4,4,4],
[5,5,5,5,5,5] ].
CubeModel.h
#ifndef CUBEMODEL_H_INCLUDED
#define CUBEMODEL_H_INCLUDED
#include <iostream>
class CubeModel
{
private:
const unsigned short m_faces;
const unsigned short m_fields;
char **m_cube_base_pointer;
public:
CubeModel(const unsigned short faces, const unsigned short fields);
~CubeModel();
void output();
};
#endif // CUBEMODEL_H_INCLUDED
CubeModel.cpp
#include "CubeModel.h"
CubeModel::CubeModel(const unsigned short faces, const unsigned short fields): m_faces(faces), m_fields(fields) {
m_cube_base_pointer = new char*[m_faces];
for (unsigned int i = 0; i < m_faces; ++i) {
m_cube_base_pointer[i] = new char[m_fields * m_fields];
memset(m_cube_base_pointer[i], i, sizeof m_cube_base_pointer[i]);
}
}
CubeModel::~CubeModel() {
for (unsigned int i = 0; i < m_faces; ++i) {
std::cout << (int) m_cube_base_pointer[i][0];
delete [] m_cube_base_pointer[i];
}
delete [] m_cube_base_pointer;
}
/*
Console output of the cube model
*/
void CubeModel::output() {
for (unsigned int i = 0; i < m_faces; ++i) {
for (unsigned int j = 0; j < m_fields * m_fields; ++j) {
std::cout << (int) m_cube_base_pointer[i][j] << std::endl; // output the model
}
}
}
main.cpp
#include <iostream>
#include "CubeModel.h"
using namespace std;
int main() {
CubeModel cube = CubeModel(6, 3);
cube.output();
system("PAUSE");
return 0;
}
When I create a CubeModel object in the main function and call the output method, I got the following error message in Visual Studio:
Exception raised at 0x00FC1DC8 in Cube.exe: 0xC0000005: Access violation at reading a position 0x00000000.
The exception is raised inside the output() method in CubeModel.
What I'm doing wrong here?

Answer 1

The third argument of memset is the number of bytes you want to set.
However
sizeof m_cube_base_pointer[i]
will give you the size of the pointer, not the size of the dynamic array you just allocated. So in order to get the right number of bytes you want to set, you should do
sizeof(char) * m_fields * m_fields
instead. And your memset call should become this:
memset(m_cube_base_pointer[i], i, sizeof(char) * m_fields * m_fields);