Segmentation Fault while Multiplying Matrices - c++

Question

for some reason, I seem to be having an exception whenever I call the following (assume A,B & C are all matrices, and that no matrix multiplication rules are broken):
c=a*b;
I have been stepping through my code for hours now, and cannot for the life of me find whats wrong.
any takers? I think it might be an issue with either the allocate() or clear() functions, or the copy constructor/assignment operator.
Thanks in advance!
// matrix.h
#ifndef matrix_H
#define matrix_H
#include <iostream>
#include <cstdlib>
using namespace std;
template <class mType> class matrix {
public:
matrix() : N(0), M(0), origin(NULL) { /* EMPTY */ }
matrix(const matrix<mType> &m) {
if (origin)
clear();
origin = new mType* [m.numrows()];
for (int i=0; i<m.numrows(); ++i)
origin[i] = new mType[m.numcols()];
}
matrix(int n, int m): N(n), M(m), origin(NULL) {
allocate(n,m);
}
~matrix() {
clear();
}
matrix & operator=(const matrix &rhs) {
if (this != &rhs) { //Check to see they're not the same instance
this->clear();
this->allocate(rhs.numrows(), rhs.numcols());
for(int i=0; i<N; ++i)
for (int j=0; j<M; ++j)
this->origin[i][j] = rhs[i][j];
}
return *this;
}
matrix & operator+=(const matrix &rhs) {
try {
if ( this->numrows() != rhs.numrows() ||
this->numcols() != rhs.numcols() )
throw 1;
}
catch (int e)
{
cerr << "Error: The addition of two matrices of different demensions is not defined." << endl;
return *this;
}
for(int i=0; i<N; ++i)
for (int j=0; j<M; ++j)
this->origin[i][j] += rhs[i][j];
return *this;
}
const matrix operator+(const matrix &rhs) const {
matrix tmp = *this; // tmp copy so we can use the += operator
return (tmp += rhs); // return answer
}
friend const matrix operator*(const matrix &that, const matrix &rhs) {
try {
if ( that.numcols() != rhs.numrows() )
throw 1;
}
catch (int e)
{
cerr << "Error: matrix Multiplication not defined." << endl;
return that;
}
matrix<mType> returnmatrix(that.numrows(), rhs.numcols());
int x=0;
for (int i=0; i<returnmatrix.numrows(); ++i)
for (int j=0; j<returnmatrix.numcols(); ++j)
for (int k=0; k < that.numcols(); ++k){
cout << (++x)<<endl;
returnmatrix[i][j] += that[i][k] * rhs[k][j];}
cout << "rt" <<endl;
return returnmatrix;
}
inline int const numrows() const {
return N;
}
inline int const numcols() const {
return M;
}
void allocate(int n, int m) {
if (origin)
clear();
origin = new mType* [n];
for (int i=0; i<n; ++i)
origin[i] = new mType[m];
M=m;
N=n;
}
void clear() {
if (this->origin) {
for(int i = 0; i < N; i++)
delete[] origin[i];
delete this->origin;
}
M=N=0; // Reset
origin=NULL;
}
mType* operator [] (const int index) { return origin[index]; }
const mType* operator [] (const int index) const { return origin[index]; }
friend matrix<mType> operator*( mType factor, const matrix<mType> rhs ) {
matrix<mType> out(rhs.numrows() , rhs.numcols());
for (int i=0; i<rhs.numrows(); ++i) {
for (int j=0; j<rhs.numcols(); ++j) {
out[i][j] = rhs[i][j]*factor;
}
}
return out;
}
friend ostream& operator<< (ostream& out, const matrix<mType>& A) {
if (A.numrows() > 0 && 0 < A.numcols()) {
out <<"[";
for (int j=0; j<A.numcols(); ++j) {
out << A[0][j] << " ";
}
for (int i=1; i<A.numrows(); ++i) {
out << endl;
for (int j=0; j<A.numcols(); ++j) {
out << " " << A[i][j];
}
}
out << "]" <<endl;
}
return out;
}
friend istream& operator>> (istream& in, matrix<mType> &A) {
//[3 2 9 1 2 3 4 5]
//toss first char
try {
if (in.get() != '[')
throw 1;
int N, M;
mType tmp;
in >> N;
in >> M;
A = matrix<mType>(N,M);
for (int i=0; i<N; ++i)
for (int j = 0; j < M; j++)
{
in >> tmp;
A[i][j] = tmp;
}
in.get();
in.ignore();
}
catch (int e) {
cerr << "Invalid Input for matrix" << endl;
}
return in;
}
private:
int N, M;
mType ** origin;
};
#endif
REVISED:
// matrix.h
#ifndef matrix_H
#define matrix_H
#include <iostream>
#include <cstdlib>
using namespace std;
template <class mType> class matrix {
public:
matrix() : N(0), M(0), origin(NULL) { /* EMPTY */ }
matrix(const matrix<mType> &m) {
origin = new mType* [m.numrows()];
for (int i=0; i<m.numrows(); ++i)
origin[i] = new mType[m.numcols()];
for (int i=0; i<N;++i)
for (int j = 0; j < M; j++)
{
origin[i][j] = m[i][j];
}
}
matrix(int n, int m): N(n), M(m), origin(NULL) {
allocate(n,m);
for (int i=0; i<N;++i)
for (int j = 0; j < M; j++)
{
origin[i][j] = 0;
}
}
~matrix() {
clear();
}
matrix & operator=(const matrix &rhs) {
if (this != &rhs) { //Check to see they're not the same instance
this->clear();
this->allocate(rhs.numrows(), rhs.numcols());
for(int i=0; i<N; ++i)
for (int j=0; j<M; ++j)
this->origin[i][j] = rhs[i][j];
}
return *this;
}
matrix & operator+=(const matrix &rhs) {
try {
if ( this->numrows() != rhs.numrows() ||
this->numcols() != rhs.numcols() )
throw 1;
}
catch (int e)
{
cerr << "Error: The addition of two matrices of different demensions is not defined." << endl;
return *this;
}
for(int i=0; i<N; ++i)
for (int j=0; j<M; ++j)
this->origin[i][j] += rhs[i][j];
return *this;
}
const matrix operator+(const matrix &rhs) const {
matrix tmp = *this; // tmp copy so we can use the += operator
return (tmp += rhs); // return answer
}
friend const matrix operator*(const matrix &that, const matrix &rhs) {
try {
if ( that.numcols() != rhs.numrows() )
throw 1;
}
catch (int e)
{
cerr << "Error: matrix Multiplication not defined." << endl;
return that;
}
matrix<mType> returnmatrix(that.numrows(), rhs.numcols());
int x=0;
for (int i=0; i<returnmatrix.numrows(); ++i)
for (int j=0; j<returnmatrix.numcols(); ++j)
for (int k=0; k < that.numcols(); ++k){
cout << (++x)<<endl;
returnmatrix[i][j] += that[i][k] * rhs[k][j];}
cout << "rt" <<endl;
return returnmatrix;
}
inline int const numrows() const {
return N;
}
inline int const numcols() const {
return M;
}
void allocate(int n, int m) {
if (origin)
clear();
origin = new mType* [n];
for (int i=0; i<n; ++i)
origin[i] = new mType[m];
M=m;
N=n;
}
void clear() {
if (this->origin) {
for(int i = 0; i < N; i++)
delete[] origin[i];
delete this->origin;
}
M=N=0; // Reset
origin=NULL;
}
mType* operator [] (const int index) { return origin[index]; }
const mType* operator [] (const int index) const { return origin[index]; }
friend matrix<mType> operator*( mType factor, const matrix<mType> rhs ) {
matrix<mType> out(rhs.numrows() , rhs.numcols());
for (int i=0; i<rhs.numrows(); ++i) {
for (int j=0; j<rhs.numcols(); ++j) {
out[i][j] = rhs[i][j]*factor;
}
}
return out;
}
friend ostream& operator<< (ostream& out, const matrix<mType>& A) {
if (A.numrows() > 0 && 0 < A.numcols()) {
out <<"[";
for (int j=0; j<A.numcols(); ++j) {
out << A[0][j] << " ";
}
for (int i=1; i<A.numrows(); ++i) {
out << endl;
for (int j=0; j<A.numcols(); ++j) {
out << " " << A[i][j];
}
}
out << "]" <<endl;
}
return out;
}
friend istream& operator>> (istream& in, matrix<mType> &A) {
//[3 2 9 1 2 3 4 5]
//toss first char
try {
if (in.get() != '[')
throw 1;
int N, M;
mType tmp;
in >> N;
in >> M;
A = matrix<mType>(N,M);
for (int i=0; i<N; ++i)
for (int j = 0; j < M; j++)
{
in >> tmp;
A[i][j] = tmp;
}
in.get();
in.ignore();
}
catch (int e) {
cerr << "Invalid Input for matrix" << endl;
}
return in;
}
private:
int N, M;
mType ** origin;
};
#endif

Answer 1

Quite a lot of code but I just looked at the copy constructor and it has two serious mistakes in it.
First mistake
matrix(const matrix<mType> &m) {
if (origin)
clear();
origin is uninitialized at this point, so you cannot test it's value. Just remove these two lines. Remember a constructor initializes a new object, it's wrong if a constructor is testing the object for what is already there.
Second mistake
Your copy constructor doesn't copy anything! It creates a matrix of the right size but it doesn't copy the matrix values!
I would guess the first error is the cause of your crash, the second error will just mean you get garbage results.