Thread: Question

Hey guys, I just need some help thinking through a line of code:

words = (char **)malloc(sizeof(char *)*TOTAL*TOTAL);

I know that you'd need to cast (char*) onto malloc() to allocate memory for chars - but why is a 2-dimensional pointer necessary? The values (TOTAL) multiplying the malloc() value just creates a larger value - not a 2-dimensional one, right?

Sorry, I should have included the variables and values in the code I posted.

#define TOTAL (100 )

char **words;

Originally Posted by brewbuck

The variable name "words" would imply an array of pointers to words, in other words, a pointer to a char pointer, so the cast to char ** makes sense. Why it is allocated to an array of TOTAL*TOTAL elements, there is no way of knowing without more code.

Would it make sense if 'words' was not an array? Because it looks like it's just a 2D pointer.

Originally Posted by MK27

Wow, would it ever. It doesn't matter what 'words' is -- you are just assigning it a block of memory of a specific size. As long as it's a pointer.

So assigning a block of memory to a 2D pointer differs from a 1D how? I'm not sure I see the benefit of 2D vs. 1D in memory assignment because there is no data structure being defined.

Originally Posted by Cell

Would it make sense if 'words' was not an array? Because it looks like it's just a 2D pointer.

"words" is a pointer to a pointer to char not a 2D pointer.

Originally Posted by Cell

This statement defines 'words' to be a pointer to a pointer. But doesn't there have to be an initial location pointed to? Wouldn't a 'pointer to a pointer' include a pointer?

That's why the return value from malloc() is cast appropriately.

Originally Posted by Cell

Since 'words' is already a pointer to a pointer, malloc() needs to be casted to a pointer to a pointer.

Exactly!

Originally Posted by Cell

Is there a name for a pointer to a pointer? It's a mouthful.

I suppose you could call it a double indirect pointer since it has two levels of indirection.