{Re-posted} How do you implement a parameter in C which can accept a pointer to a pointer which can point to any data type?

Question

void k(void** p) {
// TEST
return;
}

int main() {
int a = 6;
int* p = &a;
k(&p);
// Shows a warning
}

Answer 1

Just cast &p to void** explicitly.
k( (void**) &p );

Answer 2

@Martin Taylor
You are correct. But I just wanted to point out that the OP is asking about C, not C++. So the C compiler gives a warning, unlike the C++ compiler which gives an error.

Answer 3

Martin Taylor Thank you for the explanation. It really helps.

Answer 4

XXX and Martin Taylor Thanks for answering my question. But why in the first place does my code show a warning, i.e., why can't I pass a pointer to an int pointer as the argument to the void** parameter? @Martin Taylor, why did you typecast the resultant pointer of each of the variables to a void pointer, as the void pointer 'p' just stores the memory location and '&a' returns exactly that?

Answer 5

Martin Taylor Thank you for the explanation, and the code bits. However, my question remains unresolved. Framing it again, why does C raise a warning, if a pointer to an int pointer (or a char pointer) is provided as the argument to the function 'k' containing void** as it's parameter? Why typecast it first, as a pointer which points to another pointer pointing to an undefined type should in theory accept another pointer to an int pointer? Is there a reason for this or is it that C was made to function like this?