Cannot convert from *const to & in += operator [closed] - c++

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I was staring at this all night before I decided to give up and go to sleep - a few hours into it again today, I still don't have it. I am unable to figure out how to change the const-ness and parameters to correctly return (on the operator+=). Any help?
The error pops up at the return this statement in the operator+= overload.
#include <iostream>
#include <vector>
template <typename T> class Matrix {
private:
unsigned rows, cols;
public:
Matrix();
~Matrix();
Matrix(const Matrix<T>& rhs);
Matrix(unsigned _rows, unsigned _cols);
std::vector<std::vector<T>> matrix;
Matrix<T>& operator=(Matrix<T> rhs);
//Matrix mathematical operations
Matrix<T> operator+(const Matrix<T>& rhs);
Matrix<T>& operator+=(const Matrix<T>& rhs);
// Access the individual elements
T& operator()(const unsigned& row, const unsigned& col);
const T& operator()(const unsigned& row, const unsigned& col) const;
// Access the row and column sizes
unsigned get_rows() const;
unsigned get_cols() const;
void swap(Matrix<T>& rhs);
};
template<typename T>
Matrix<T>::Matrix() {}
template<typename T>
Matrix<T>::~Matrix() {}
// Parameter Constructor
template<typename T>
Matrix<T>::Matrix(unsigned _rows, unsigned _cols) {
matrix.resize(_rows);
for (unsigned i = 0; i < _rows; i++)
matrix[i].resize(_cols, 1); // change back to 0 after debug
rows = _rows;
cols = _cols;
}
template<typename T>
Matrix<T>& Matrix<T>::operator=(Matrix<T> rhs) {
swap(rhs);
return *this;
}
template<typename T>
Matrix<T> Matrix<T>::operator+(const Matrix<T>& rhs) {
Matrix<T> result(*this);
result += rhs;
return result;
}
template<typename T>
Matrix<T>& Matrix<T>::operator+=(const Matrix<T>& rhs) {
for (unsigned i = 0; i < rows; i++) {
for (unsigned j = 0; j < cols; j++) {
this->matrix[i][j] += rhs(i, j);
}
}
return this; // error pops up here
}
// Access the individual elements
template<typename T>
T& Matrix<T>::operator()(const unsigned& row, const unsigned& col) {
return this->matrix[row][col];
}
// Access the individual elements (const)
template<typename T>
const T& Matrix<T>::operator()(const unsigned& row, const unsigned& col) const{
return this->matrix[row][col];
}
// Get the number of rows of the matrix
template<typename T>
unsigned Matrix<T>::get_rows() const {
return this->rows;
}
//Get the number of columns of the matrix
template<typename T>
unsigned Matrix<T>::get_cols() const {
return this->cols;
}
template<typename T>
void Matrix<T>::swap(Matrix<T>& rhs) {
using std::swap;
swap(this->rows, rhs.rows);
swap(this->cols, rhs.cols);
swap(this->matrix, rhs.matrix);
}
// for debugging
template<typename T>
void print_matrix(Matrix<T>& matrix) {
for (int i = 0; i < matrix.get_rows(); i++) {
for (int j = 0; j < matrix.get_cols(); j++) {
std::cout << matrix(i, j) << " ";
}
std::cout << " " << std::endl;
}
}
int main(int argc, char **argv) {
Matrix<double> matrix1(5, 5);
Matrix<double> matrix2(5, 5);
// Start testing
Matrix<double> matrix3 = matrix1 + matrix2;
print_matrix(matrix1);
std::getchar();
return 0;
}

Answer 1

In the += operator, you probably want:
Matrix<T>& Matrix<T>::operator+=(const Matrix<T>& rhs) {
//....
return *this;
//^^
}
The linker error is because you did not define:
Matrix(const Matrix<T>& rhs);