Operator Overloading

[paragdhungana]

I have a designed a class Matrix and i want to overload the + and * operators to add and multiply 2 matrices.

My code is as follows:

#include <iostream>
#include <string>
#include <stdio.h>

using namespace std;



class Matrix
//CREATES A MATRIX
{
      double** m;  
      string name; 
      int rows, columns; 
      public:
        Matrix (){}
        Matrix(int r, int c, string n = "anonymous")             
        {    
             name=n;
             rows = r;
             columns = c;
             try { m = new double *[rows]; } catch (exception e) { if (m==0){cout<<"error";}}   
             for ( int i = 0; i <rows; i++)
             {
                try { m[i] = new double [columns];} catch (exception e) { if (m[i]==0){cout<<"error";}} 
             } 
        }
        ~Matrix(); //~Matrix(){ cout<<"\n"<<name<<" deleted"; delete m;};
        
        Matrix operator+ (const Matrix x)
        //overload the + operator
        {               
              if ( x.rows != this.rows )
              {
                  cout<<"Error: Rows are not equal";
                  return 0;
              }
              if (x.columns != this.columns)
              {
                  cout<<"Error: Columns are not equal";
                  return 0;
              }
              Matrix c( x.rows,x.columns);   
              for (int i = 0; i < rows; i++)
              {
                  for (int j=0; j < columns; j++)
                  {
                      c.m[i][j] = x.m[i][j]+this.m[i][j];
                  }
              }          
        }
        
  ...
  ...
}

I get a strange error in the lines 33 and 38 as shown below, which says
" In member function `Matrix Matrix::operator+(Matrix)': `rows' is not a type request for member of non-aggregate type before ')' token . conversion from `int' to non-scalar type `Matrix' requested "
and similarly same error for column variables too.

rows and columns are the members of class Matrix and since x is a parameter of type Matrix, there shouldn't be any reason why i shouldn't be able to access the private variable from its member function

if ( x.rows != this.rows )
              {
                  cout<<"Error: Rows are not equal";
                  return 0;
              }
              if (x.columns != this.columns)
              {
                  cout<<"Error: Columns are not equal";
                  return 0;
              }

[paragdhungana]

i have solved my problem...
it was because i used this to reference a member variable.

[Zhuge]

Maybe it was because you were doing this.var rather than this->var? this is a pointer to the current instance.

[jsmith]

Just a couple of other things...

operator+() should take its parameter by const& and the member function itself should be const. Also it does not appear to return anything.

The default constructor does not initialize the m pointer to anything.

Catch by const reference, not by value.

Your catch block appears to try to catch out-of-memory errors. Two things:
1) If you are out of memory, be aware that operator<<() may also attempt to allocate memory, so your cout could itself throw.
2) std::bad_alloc is throw on new failure. Catch that and then you don't have to check the pointer. Because if you want to check the pointer, you have to assign it 0 before doing the new[], because in the event that new throws, m will contain its original value, which is undefined since you don't pre-initialize it.