How can I convert a int 2d array initialized liked this:
int 2darray[9][9];
Into a void * then back to a 2d array again. This one gives me an incompatible pointer type error
int **sub = *((int **)2darray);
1 Answer
The cast to int** should be like this:
int **sub = ((int **)2darray);
You can not cast the pointer back to an array, it just doesn't make sense. You can, however, cast the pointer back to an array-pointer as shown here https://stackoverflow.com/a/20046703/6024122. As noted in that answer, this is quite uncommon, I've never personally witnessed it.
ETA: pthread_create requires its parameter to be a void *arg, thus you should do something like this:
pthread_create(..., (void *) 2darray);
and then
int **ptr = (int**) arg;
5 Comments
Kishore Bandi
Well, I agree with the part where it may not make sense. However its valid to convert array to pointer. Internally they're the same. You can check my comment for the sample code which will compile successfully.
Patrick Trentin
Converting array to pointer does make sense, what it does not make sense is pointer to array, it's not even possible. At best you can convert it into array pointer, to the best of my knowledge.
Kishore Bandi
Sorry, I meant pointer to array itself. Its completely valid. Like I said they're treated the same at the end of the day for processing. They access the address directly and increment based on the basic bytes allocated. Example:
int a[2]; // Initialize with something. you can cout << *(a+1) this is equal to cout << a[1]. Similarly you can assign a pointer to array to array to pointer as well.Patrick Trentin
I am afraid we are not talking about the same thing, that's just how you resolve pointer indexing. I mean actually doing something like int a[2] = ptr;
Kishore Bandi
Okay, you're right. we were on different context. I was talking about conversion and access. never mind.
int darray[9][9];void *sub = darray;int **subInt = (int **)sub;AFAIK, Variable cannot start with a number. Its always a character or $ or _