C Programming: malloc() for a 2D array (using pointer-to-pointer)
- by vikramtheone
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);
}
