return 2d array to caller from public class function

[Cosa]

Hi, I am having a problem with returning a 2d array back to the main in my program. The program reads in a matrix from a file, then it has to multiply etc, however i cannot get the print function to work since the array that is made in the load function is passed back to the main. Here is my code, i am being told that the array i want to print is undefined. I cannot change any of the public member functions, however i can add to the private, but i dont see how that would help me print.

matrix.h

#include <iostream>
#include <fstream>
using namespace std;

#ifndef _matrix_H_
#define _matrix_H_

class matrix
{
	public:
		matrix();// constructor
		matrix(const matrix&);// copy constructor
		~matrix();// destructor
		
		bool multiply(const matrix&, const matrix&);
		bool isequal(const matrix&);
		bool copy(matrix&);
		bool load(istream&);
		void print(ostream&);
		bool isset() const;
		void getrowscols(int&, int&) const;
	private:
		int rows;// number of rows
		int cols;// no of columns
		float** data;// 2 dimensional array
};

#endif

main.cpp

#include <iostream>
#include <fstream>
#include "matrix.h"
using namespace std;

int main()
{
	char filename[50];	

	matrix* ob;
	ob = new matrix();

	matrix ob2;
	

	cout << "Enter filename to open: " << endl;
	cin >> filename;

	fstream ins;
	ins.open(filename, ios::in | ios::out);

	ob2.load(ins);
	ob2.print(ins);

	ins.close();

	return 0;
}

matrix.cpp

#include <iostream>
#include <fstream>
#include "matrix.h"
using namespace std;

matrix::matrix()
{
	rows = 0;
	cols = 0;
	
	data = new float *[rows];
	for(int i = 0; i < rows; i++)
		*(data+i) = new float [cols];
}

matrix::matrix(const matrix& p)
{
	rows = p.rows;
	cols = p.cols;

	data = new float *[rows];
	for(int j = 0; j < rows; j++)
		*(data+j) = new float [cols];

	for(int i = 0; i < rows; i++)
		for(int j = 0; j < cols; j++)
			*(*(data+i)+j) = *(*(p.data+i)+j);
}

matrix::~matrix()
{
	for(int i = 0; i < rows; i++)
		delete [] *(data+i);
	delete [] data;
}

bool matrix::load(istream& ins)
{
		ins >> rows >> cols;			//read in rows and columns

		float** array = new float*[rows];	//create matrix
		
		if (array != NULL) 
		{
			for (int i = 0; i < rows; i++)		
			{
				array[i] = new float[cols];
  			}
		}

		for (int i = 0; i < rows; i++)			//read in data
		{
			for (int j = 0; j < cols; j++)
			{
			ins >> array[i][j];
			}		
		}
	return array;
	return true;
}

void matrix::print(ostream& ins)
{
	for(int i = 0; i < rows; i++)			//print function
	{
		for(int j = 0; j < cols; j++)
		{
			ins << " " <<  array[i][j];
		}
		cout << endl;
	}

}

[Nick Evan]

bool matrix::load(istream& ins)
{
[....more code....]
	return array;
	return true;
}

You can't return array because the function can only return a bool. So it will return 'true' because the memory-address of array != 0

Why don't you just use the private float** data; to store the data in matrix::load?

[Cosa]

when i use the private float** data i get a segementation fault.

[Nick Evan]

That's probably because of this:

matrix::matrix()
{
	rows = 0;
	cols = 0;
	
	data = new float *[rows];

Since there aren't any rows (rows = 0) you can't store data in it.

[Cosa]

bool matrix::load(istream& ins)
{
		ins >> rows >> cols;
...

I read in the size of the matrix from the file

[Cosa]

Thanx for the help, i got it to work using data.

[Nick Evan]

[edit] Great!