运算符重载+动态矩阵

Question

So I have decided to restart my program everything except the + operator is working now. I get the read access violation exception

Header File

#pragma once
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

class MatrixType
{
private:
    int **matrix;
    int row;
    int col;
public:
    void setElement(int r, int c, int newvalue);
    void display();

    const MatrixType& operator=(const MatrixType& mat);
    MatrixType operator+(const MatrixType& mat) const;

    friend std::ostream & operator << (std::ostream & out, const MatrixType & mat);

    MatrixType(int r, int c);
    MatrixType(string fileName);
    MatrixType(const MatrixType& mat);
    MatrixType();
    ~MatrixType();
};

Implementation File

#include "matrixType.h"
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

void MatrixType::setElement(int r, int c, int newvalue)
{
    matrix[r][c] = newvalue;
}

void MatrixType::display()
{
    for (int i = 0; i < row; i++)
    {
        for (int r = 0; r < col; r++)
            cout << matrix[i][r] << " ";
        cout << endl;
    }
    cout << endl;
}

const MatrixType& MatrixType::operator=(const MatrixType& mat)
{
    if (row != mat.row)
    {
        cout << "The matrixes are not identical" << endl;
        return *this;
    }
    for (int i = 0; i < row; i++)
    {
        for (int r = 0; r < col; r++)
        {
            matrix[i][r] = mat.matrix[i][r];
        }
    }
    return *this;
}

MatrixType MatrixType::operator+(const MatrixType& mat) const
{
    MatrixType tempMatrix;
    if (row != mat.row)
    {
        cout << "The matrixes are not identical can not be added together" << endl;
        return *this;
    }
    else
    {
        for (int i = 0; i < mat.row; i++)
        {
            for (int r = 0; r < mat.col; r++)
            {
                tempMatrix.matrix[i][r] = mat.matrix[i][r] + matrix[i][r];
            }
        }
        return tempMatrix;
    }
}

std::ostream & operator << (std::ostream & out, const MatrixType & mat)
{
    for (int i = 0; i < mat.row; i++) {
        for (int j = 0; j < mat.col; j++) {
            out << mat.matrix[i][j] << "  ";
        }
        out << std::endl;
    }
    return out;
}

MatrixType::MatrixType(int r, int c)
{
    matrix = new int*[r];
    for (int i = 0; i < r; i++)
    {
        matrix[i] = new int[c];
    }
    row = r;  
    col = c;
    for (int i = 0; i < row; i++)
    {
        for (int s = 0; s < col; s++)
        {
            matrix[i][s] = 0;
        }
    }
}
MatrixType::MatrixType(string fileName)
{
    int r;
    int c;
    int z;
    ifstream myFile;
    myFile.open(fileName);
    myFile >> r;
    myFile >> c;
    matrix = new int*[r];
    for (int i = 0; i < r; i++)
    {
        matrix[i] = new int[c];
    }

    for (int i = 0; i < r; i++)
    {
        for (int s = 0; s < c; s++)
        {
            myFile >> z;
            matrix[i][s] = z;
        }
    }
    row = r;
    col = c;
    myFile.close();
}

MatrixType::MatrixType(const MatrixType& mat)
{
    row = mat.row;
    col = mat.col;
    matrix = new int*[row];
    for (int i = 0; i < row; i++)
    {
        matrix[i] = new int[col];
    }
    for (int i = 0; i < row; i++)
    {
        for (int s = 0; s < col; s++)
        {
            matrix[i][s] = mat.matrix[i][s];
        }
    }
}

MatrixType::MatrixType()
{
}

MatrixType::~MatrixType()
{
    for (int i = 0; i < row; i++)
    {
        delete[] matrix[i];
    }
    delete[] matrix;
}

Source Code

#include "MatrixType.h"
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

int main()
{
    MatrixType M1("matrixfile1.txt");
    MatrixType M2("matrixfile2.txt");
    MatrixType M3("matrixfile3.txt");

    cout << "Matrix 1:" << endl << M1 << endl << endl;
    cout << "Matrix 2:" << endl << M2 << endl << endl;
    cout << "Matrix 3:" << endl << M3 << endl << endl;

    MatrixType M4 = M1 + M3;

    return 0;
}

So basically the goal is to check to see if the matrixes are identical otherwise you should just see a print the matrixes are not the same size. The matrixfile1,2,3 that look like

3 3

1 1 1

1 1 1

1 1 1

That show the dimensions of the array and their elements. My question is what I could do to make my operator function work better as it is currently not able to add the matrixs together yet. Everything else though once again works its just the operator that gets a read access violation.

Answer 1

MatrixType::MatrixType()
{
}

This doesn't initialize the members row , col , or matrix at all, so it's undefined behavior to attempt to use the current values of any of them.

Since you haven't provided a way to change the dimensions of a MatrixType at all, even using operator= , there doesn't seem to be any good use of a default constructor, and probably the MatrixType() default constructor shouldn't exist at all.

MatrixType MatrixType::operator+(const MatrixType& mat) const
{
    MatrixType tempMatrix;

Your operator+ starts out by initializing tempMatrix using the default constructor. So the dimensions of tempMatrix are...?