malloc and free for 2-dimensional array

[c_assassin]

Hi!

I am trying to explore skills in C, however, I think I don't have a very good background in topics such as malloc.

I am trying to convert multiple images (.bmp) into two-dimensional arrays for image processing. Importing the image and processing it one-by-one in a for-loop. I'm having trouble with managing the memory usage and the program crashes because i think it's taking so much memory. I wish to assign same memory over and over in the for-loop.

I think the problem is on how I use the malloc and the free for my two-dimensional array.
Please check if I'm using them correctly for my two-dimensional array.

int **image_matrix;

             //Allocate memory and initialize image_matrix
             image_matrix = (int **)malloc(rows * sizeof(int *));
             if (NULL == image_matrix)
             {
                      free(image_matrix);
                      printf("Memory allocation failed while allocating for the array[].\n");
                      exit(1);
             }
             image_matrix[0] = (int *)malloc(cols * rows * sizeof(int));
             for(r=1; r<rows; r++)
             {
                      image_matrix[r] = image_matrix[0] + r*cols;
             }
             for(r=0; r<rows; r++)
             {
                      for(c=0; c<cols; c++)
                      {
                               image_matrix[r][c] = 0;
                      }
             }

             //Free image_matrix
             for(r=1; r<rows; r++)
             {
                      free(image_matrix[r]);
             }
             free(image_matrix);

[Salem]

First, remove the cast on the result of malloc.
If you've included stdlib, then there is nothing more to do.

Not including stdlib.h results in the cast suppressing a potentially very serious error.


The alloc seems OK, but you have far too many free calls.
All you need is
free( a[0] );
free( a );