Hi Guys, yesterday I had posted a question: How should I pass a pointer to a function and allocate memory for the passed pointer from inside the called function?

From the answers I got, I was able to understand what mistake I was doing.

I'm facing a new problem now, can anyone help out with this?

I want to dynamically allocate a 2D array, so I'm passing a Pointer-to-Pointer from my main() to another function called alloc_2D_pixels(...), where I use malloc(...) and for(...) loop to allocate memory for the 2D array.

Well, after returning from the alloc_2D_pixels(...) function, the pointer-to-pointer still remains NULL, so naturally, when I try accessing or try to free(...) the Pointer-to-Pointer, the program hangs.

Can anyone suggest me what mistakes I'm doing here?

Help!!!

Vikram

SOURCE:

main()
{


 unsigned char **ptr;
 unsigned int rows, cols;

 if(alloc_2D_pixels(&ptr, rows, cols)==ERROR)      // Satisfies this condition
  printf("Memory for the 2D array not allocated"); // NO ERROR is returned

 if(ptr == NULL)                    // ptr is NULL so no memory was allocated
  printf("Yes its NULL!");          

 // Because ptr is NULL, with any of these 3 statements below the program HANGS
 ptr[0][0] = 10;                    
 printf("Element: %d",ptr[0][0]);

 free_2D_alloc(&ptr);

}


signed char alloc_2D_pixels(unsigned char ***memory, unsigned int rows, unsigned int cols)
{
        signed char status = NO_ERROR;

        memory = malloc(rows * sizeof(unsigned char** ));

        if(memory == NULL)
        {
            status = ERROR;
            printf("ERROR: Memory allocation failed!");

        }
        else
        {
            int i;

            for(i = 0; i< cols; i++)
            {
                memory[i] = malloc(cols * sizeof(unsigned char));

                if(memory[i]==NULL)
                {
                    status = ERROR;
                    printf("ERROR: Memory allocation failed!");
                }
            }

        }

    // Inserted  the statements below for debug purpose only
        memory[0][0] = (unsigned char)10;     // I'm able to access the array from
        printf("\nElement %d",memory[0][0]);  // here with no problems


        return status;
}


void free_2D_pixels(unsigned char ***ptr, unsigned int rows)
{
     int i;

     for(i = 0; i < rows; i++)
     {
          free(ptr[i]);
     }

     free(ptr);
}