Thread: passing struct by ref that was passed by ref from one function to another

Originally Posted by javaeyes

I now need to pass it again to another helper function. Do I need to pass it again by reference, or can I just pass it like a 'normal' variable, by value and derefence it.

Here's the thing: what is "it"? Is "it" your struct object, or is "it" a pointer to your struct object?

People will look at you funny if you talk about pass by reference in C; the orthodoxy is that everything is passed by value, because when you use a pointer, what you are doing is passing a memory address. Manipulating memory addresses directly is commonplace in C, so it makes sense to regard them as values, and not just references to the data they contain.

References (which do not exist in C) and pointers are not quite the same thing, because while a pointer can serve as (the equivalent of) a reference (hence, it can be dereferenced), it has more uses beyond that. So you would say, "I have a pointer to a struct which I passed to a function. I now need to pass it again to another function." If you consider that for a moment, the answer to your question should be clear.*

Do I need to pass it again by reference, or can I just pass it like a 'normal' variable, by value and derefence it. I think I can just pass it normally.

You don't need to dereference pointers to structs, you can just use pointer notation with it:

Code:

struct whatever {
    int x;
};
struct whatever a, *p = &a;
a.x = 666;  // normal struct notation uses .
p->x *= 2; // pointer to struct notation uses ->

* yes, you just pass the same address (pointer) on.

Originally Posted by javaeyes

I have struct instance in main named option. I pass it by reference like this: functionOne(&option).

Nope, you are passing the address of (&), aka a pointer to, "option". See post #3.

Originally Posted by javaeyes

I'm just doing this: myFunction(&mystruct), Is that the same thing? Thanks.

Yep. I just created a pointer to illustrate, that's not necessary for passing an address. A pointer is just a primitive type that holds a memory address (like an int holds a whole number), which is the value you are passing. Unlike references in other languages, there is nothing else under the hood. This is why a pointer is (generally) 4 bytes long on 32 bit systems and 8 bytes long on 64 bit systems.