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:

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#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;
}

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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.

Quote:

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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.

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

Quote:

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Originally Posted by Kittu20

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

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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).