Thread: classs with multiple arrays

Hi guys,

The following class keeps giving me a segmentation fault. I am trying to dynamically allocate three pointers ptr1, ptr2, ptr3. Constant Grids is equal to 20. It works if I have only one pointer.

Code:

class matrix_col { 

public:

  int i;
  double *ptr1, *ptr2, *ptr3;

  matrix_col(){

    ptr1 = new double[Grids];
    ptr2 = new double[Grids];
    ptr3 = new double[Grids];

  for(i = 0; i < (Grids); i++)

    ptr1[i] = 0;
    ptr2[i] = 0;
    ptr3[i] = 0;
}

//copy constructor
matrix_col(const matrix_col &a){

  int i;
 
    ptr1 = new double[Grids];
    ptr2 = new double[Grids];
    ptr3 = new double[Grids];

  for(i = 0; i < (Grids); i++)

    ptr1[i] = a.ptr1[i];
    ptr2[i] = a.ptr2[i];
    ptr3[i] = a.ptr3[i];
}

  ~matrix_col(){

    delete [] ptr1;
    delete [] ptr2;
    delete [] ptr3;

}

  //double index(int, int);
  void show_variable();

  //void col_insert(flow_field &, flow_field &, flow_field &);
  friend matrix_col operator+(const matrix_col &, const matrix_col &);
  friend matrix_col operator-(const matrix_col &, const matrix_col &);
  const matrix_col &operator=(const matrix_col &);
};

Shuo

i stopped looking after i noticed a first problem:

Code:

  matrix_col(){

    ptr1 = new double[Grids];
    ptr2 = new double[Grids];
    ptr3 = new double[Grids];

  for(i = 0; i < (Grids); i++)

    ptr1[i] = 0;
    ptr2[i] = 0;
    ptr3[i] = 0;
}

you probably want the three ptr statements enclosed by {}'s. if the problem still persists ill take a deeper look.. hope it helps.

I added the bracket and it worked as part of a larger code but gives the following error message.

*** glibc detected *** double free or corruption (!prev): 0x08056b08 ***
Aborted

Is it to do with the destruction of the objects?

I added some more brackets inside the class functions and the error message went away.
Thanks for your help

yes you needed both brackets.

what your for loop was doing was running and only executing the ptr1 statement, then once i was 20 it would initialize both 'ptr2[20]' and 'ptr3[20]', which isnt a good idea since your array goes from 0 - (Grids-1)

your welcome

Make sure you also implement a copy assignment operator for your class.

A better solution would be to use a vector rather than a dynamic array. You wouldn't need to worry about either of that function, and you wouldn't have to worry about the copy constructor and destructor either. Those would just work automatically.