Segmentation Fault Error Dealing with Matrices (Arrays) - c++

Question

I'm trying to reference a 2D array object I've constructed, but for whatever reason I'm getting a segmentation fault and I'm having trouble figuring out the cause. So far I've deduced that the error lies in my operator<< function, but I can't figure out what to change.
main.cpp:
int main() {
My_matrix m1(3, 2);
cout << "Before" << endl;
m1(0,0) = 1; //causes segfault
cout << "After" << endl;
m1(0,1) = 2; //causes segfault
m1(1,0) = 3; //causes segfault
m1(1,1) = 4; //causes segfault
m1(2,0) = 5; //causes segfault
m1(2,1) = 6; //causes segfault
cout << "Checkpoint 1" << endl;
My_matrix m2(); //works
cout << "Checkpoint 2" << endl;
cout << m1.number_of_rows() << endl; //works
cout << "Checkpoint 3" << endl;
cout << m1; //Segfault
cout << "Checkpoint 4" << endl;
cout << m1; //Segfault
cout << "Checkpoint 5" << endl;
cout << m2; //Segfault
cout << "Checkpoint 6" << endl;
}
My_matrix.cpp:
#include "My_matrix.h"
#include <stdexcept>
My_matrix::My_matrix()
{
n = 0;
m = 0;
ptr = nullptr;
}
My_matrix::My_matrix(int n1, int m1)
{
n = n1;
m = m1;
ptr = new int*[n];
for(int i = 0; i < n; i++) {
ptr[i] = new int[m];
}
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
ptr[i][j] = 0;
}
}
}
My_matrix::My_matrix(const My_matrix& mat)
{
this->n = mat.n;
this->m = mat.m;
ptr = new int*[n];
for(int i = 0; i < n; i++) {
ptr[i] = new int[m];
}
//----- copy elements over to new matrix -----//
for (int i = 0; i < mat.n; i++) {
for (int j = 0; j < mat.m; j++) {
this->ptr[n][m] = mat.ptr[n][m];
}
}
}
My_matrix::~My_matrix()
{
clear();
}
My_matrix& My_matrix::operator=(const My_matrix& mat)
{
clear();
this->n = mat.n;
this->m = mat.m;
ptr = new int*[n];
for(int i = 0; i < n; i++) {
ptr[i] = new int[m];
}
//----- copy elements over -----//
for (int i = 0; i < mat.n; i++) {
for (int j = 0; j < mat.m; j++) {
this->ptr[n][m] = mat.ptr[n][m];
}
}
}
int My_matrix::number_of_rows() const
{
return n;
}
int My_matrix::number_of_columns() const
{
return m;
}
int* My_matrix::operator()(int i) const
{
return ptr[i];
}
int& My_matrix::operator()(int i, int j) const
{
return ptr[n][m];
}
int& My_matrix::operator()(int i, int j)
{
return ptr[n][m];
}
int& My_matrix::elem(int i, int j) const
{
if (i < 0 || i >= n) throw out_of_range("Out of range");
if (j < 0 || j >= m) throw out_of_range("Out of range");
return ptr[n][m];
}
int& My_matrix::elem(int i, int j)
{
if (i < 0 || i >= n) throw out_of_range("Out of range");
if (j < 0 || j >= m) throw out_of_range("Out of range");
return ptr[n][m];
}
void My_matrix::clear()
{
for (int i = 0; i < n; i++) {
delete[] ptr[i];
}
delete[] ptr;
n = 0;
m = 0;
}
ostream& operator<<(ostream& out, const My_matrix& mat)
{
for (int i = 0; i < mat.number_of_rows(); i++) {
for (int j = 0; j < mat.number_of_columns(); j++) {
out << mat(i, j) << " "; //This line is the culprit ****
}
out << endl;
}
return out;
}

Answer 1

As hinted at by #WhozCraig and #O'Neil in the comments, I had a few typos in my code which referred to indices that were not in bounds of the matrix I had created. Rather than using the iterators/function arguments, I used n and m, which represent the size of the matrix, which is obviously one larger than the largest index. Examples include:
int& My_matrix::elem(int i, int j) const
{
if (i < 0 || i >= n) throw out_of_range("Out of range");
if (j < 0 || j >= m) throw out_of_range("Out of range");
return ptr[n][m]; //<--- should be return ptr[i][j];
}
as well as
My_matrix::My_matrix(const My_matrix& mat)
{
this->n = mat.n;
this->m = mat.m;
ptr = new int*[n];
for(int i = 0; i < n; i++) {
ptr[i] = new int[m];
}
//----- copy elements over to new matrix -----//
for (int i = 0; i < mat.n; i++) {
for (int j = 0; j < mat.m; j++) {
this->ptr[n][m] = mat.ptr[n][m]; //<--- should be this->ptr[i][j] = mat.ptr[i][j];
}
}
}
By correcting these discrepancies my issue was resolved.