Thread: memory freeing function

Hi!

I'm supposed to do some matrix handling functions for a school project. But i'm having trouble with function that frees memory allocated for the matrix. I use

Code:

  retMatrix=(double **)malloc(rows*sizeof(double *));
  for(i=0;i<rows;i++)
   {
    retMatrix[i]=(double *)malloc(columns*sizeof(double));
   }

to allocate the memory. And

Code:

void matrixDestruct(double **matrix)
{
   int i=0;
    while(matrix[i]!=NULL)
    {
     free(matrix[i]);
     i++;
    }  
   free(matrix);
}

to free it but the destructor gives a memory handling error when i run it my program with walgrind. I know that the problem is matrix[i]!=NULL but i cant think of any other way to determine what is the last row of the matrix. Use of global variables is not allowed. Anyone got ideas?

Originally Posted by johndoe

Hi!

Code:

void matrixDestruct(double **matrix)
{
   int i=0;
    while(matrix[i]!=NULL)
    {
     free(matrix[i]);
    }  
   free(matrix);
}

You are not updating i above, so you are trying to free matrix[0] forever.

Also, please see the casting malloc FAQ.

Also, I don't see any code in your original post that contains an explicit NULL at the end of your matrix array.

You can't just expect it to magically stop. You have to keep track of the size of your matrix. Pass it as a function argument. Either that, or allocate an extra pointer, for the "row", set it to NULL, and stop when you reach it. Of course if you forget to set it to NULL, you're hosed.


Quzah.