Thread: Pointer to structure

Can someone confirm if I am thinking right. If I want to change value of pointer so I think I need to pass address of pointer not the copy of pointer

Code:

#include<stdio.h>

#include<stdlib.h>


struct s
{
	int var;
};


int main ()
{
	struct s *sp = NULL;
	
	foo(&sp); // Pass address of sp to function foo
	foo(sp);  // Pass copy of sp  to function foo
	
	return 0;
}

Yes that is correct.. If you need to change the value of the pointer variable(via a function call), then you pass the address of the variable pointer.

Originally Posted by G4143

Yes that is correct.. If you need to change the value of the pointer variable(via a function call), then you pass the address of the variable pointer.

Why there is need to declare double pointer as argument, not just pointer to structure to change variable sp

Originally Posted by Kittu20

Why there is need to declare double pointer as argument, not just pointer to structure to change variable sp

You pass a pointer to a pointer because you need to pass the original variable address which is a pointer... Clear as mud right?

It all comes down to what is passed to the function "copied" and what the copied values represent.

The biggest hurdle here is understanding that C functions pass by value(i.e. it copies the value).