Can't read char array - c++

Question

The basic problem is that we (in pairs) have been tasked with creating a program to - amongst other things - read in a txt file and display it as a sudoku board as part of our introduction to coding at Uni.
We have completed most of the code and have got it working sufficiently well. However, we are struggling with what I would consider to be a basic aspect of this. The code reads in the file and saves it to the classes private char 9*9 matrix. We have run a debugging print-out to check that the values are being saved to the matrix and this is indeed the case. The issue is with the getMatrixVal(int x, int y) function which we think is returning a pointer rather than the character. We have tried returning a pointer from the function and have tried saving to a pointer and then to a char variable. Unfortunately, we am not excellent on pointer's.
With the recent suspensions to University timetables, we are temporarily unable to get the advice and support we require and, hence, we are applying here for advice.
Also, we are using the qt programming software on a raspberry pi - could this have anything to do with our problems?
#include "grid.h"
#include <QDebug>
#include <QChar>
#include <QFile>
grid::grid(char matrix_value, const int x, const int y) {
matrix[x][y] = matrix_value;
//char c = matrix[x][y];
//qDebug() << QChar(c);
}
void grid::load_file() {
QFile file("/home/pi/Documents/ELEC1204/P6/SUDOKU.txt");
char character, c;
int i, j;
if(!file.open(QFile::ReadOnly)) {
qDebug() << "Error in opening file";
return;
} //Print error if message if unable to open file
for(i = 0; i < 9; i++) {
for(j = 0; j < 9; j++) {
SKIP: //Related to 'goto'
file.read(&character, sizeof(char)); //Read ini individual characters
if(character == '\xd' || character == '\xa')
goto SKIP;
//Skip character related to new lines
//Goes to 'SKIP' point in program
else if(character == 'X')
grid('_', i, j);
//Save 'X's as '_'
else
grid(character, i, j);
//Save numbers as they are
c = getMatrixVal(i, j);
qDebug() << "i = " << i << "| j = " << j << "| Character is: " << QChar(character) << "| Matrix character is: " << QChar(c);
//Print-out for debugging
}
}
file.close();
//Close file
}
// Possibly useful source:
// https://doc.qt.io/qt-5/qfile.html
// https://forum.qt.io/topic/60240/reading-file-byte-by-byte/5
char grid::getMatrixVal(const int x, const int y) {
char c = matrix[x][y];
//qDebug() << "Matrix[" << x << "][" << y << "] is: " << QChar(c);
return c;
}
void grid::printMatrix() {
for(int i = 0; i < 9; i++) {
for(int j = 0; j < 9; j++) {
qDebug() << matrix[i][j];
}
}
}
//Prints out matrix
//Debugging function

Answer 1

There is nothing wrong with getMatrixVal: it returns a character from the right place in matrix.
Your call grid(character, i, j) constructs a new grid instance that is unrelated to the current one.
Instead, just assign directly to matrix: (or use a setter function)
matrix[i][j] = character;