Pointer to void

A pointer to void is used to hold references to any data type. It has two properties:

• Pointer to void has the same representation and memory alignment as pointer to char.
• Pointer to void is never equal to another pointer but two void pointers assigned to a NULL are equal. The behavior of void pointers is system dependent.

We can assign any pointer to a pointer to void. We must be careful when we cast an arbitrary pointer to a pointer to void because there is nothing that prevents you from casting it to a different pointer type afterwards.

int main(void)
{
	int	number;
	int	*ptr;
	void *ptrvoid;

	printf("Address of ptr: %p\nAdress of ptrvoid %p\n", ptr, ptrvoid);
	number = 10;
	ptrvoid = &number;
	printf("Adress of ptrvoid %p\n", ptrvoid);
	ptr = (int *)ptrvoid;
	printf("Address of ptr: %p\nAdress of ptrvoid %p\nValue pointed to by a pointer variable ptr: %d\n", ptr, ptrvoid, *ptr);
	return (0);
}

Terminal$ gcc PointerToVoid.c
Terminal$ ./a.out
Address of ptr: 0x64
Adress of ptrvoid 0x1000
Adress of ptrvoid 0x7ffc8d6da404
Address of ptr: 0x7ffc8d6da404
Adress of ptrvoid 0x7ffc8d6da404
Value pointed to by a pointer variable ptr: 10

We can use sizeof operator with a pointer to void as shown below:

size_t	size = sizeof(void*);

Size_t is a data type that is used for size of an object as a number of bytes. It is generally equivalent to unsigned int and is contained in header files stddef.h or stdio.h.

Sources:
[1] Understanding and Using C Pointers by Richard Reese (O’Reilly). Copyright 2013 Richard Reese, Ph.D. 978-1-449-34418-4
[2] PRINZ, Peter a Ulla KIRCH-PRINZ. C Pocket Reference. O’REILLY, 2003. ISBN 978-0-596-00436-1.