Further clarification on structs and pointers, please.

[SeldinG]

I've been lurking online for some more information on Structs and Pointers. I use them all the time for various things depending on what my needs are. I just want to make sure my thoughts line up with the way things should be and there are a few that I'm iffy on.

I've read that if you just create a struct...

struct OBJECT{
    int x,y;
}myobject;

...whenever you want to call upon that struct you have to always prefix it with struct myobject before using it. I've never done this. I just call the member

myobject.x

And I've never had an issue doing it this way. Also I use typedef depending on my needs. However, according to what I have read, typedef just masks the namespace and the member id to read as the same thing.

typedef struct OBJECT{
   int x,y;
}OBJECT;

Again, according to the books it makes it so you don't have to write the word struct before calling your struct each time. Like I said, I've never had to write struct more than once for each declaration so I'm not so sure about that. Maybe it's old and that's why I don't see that use anymore? But in any case, I've also never had an issue with not using typdef on a struct and declaring it like this:

struct OBJECT{ // <---notice no typedef
   int x,y;
}OBJECT;

The above seems to work just fine as well.


My second area is on the use of pointers, specifically with structs. In general I use * for a pointer and & when creating a pointer reference or accessing its address. But I've seen pointers without any operator being used. Example:

typedef struct OBJECT{
  int x,y;
}OBJECT;

OBJECT *chair; // using *

// or

OBJECT &chair; // using &

// or

OBJECT chair; // no operator

While I have used all three ways, I am not so sure as of the last one and I can't find any good documentation on it other than the few times I've seen it used without much explanation.

Thanks a bunch.

[jimblumberg]

struct OBJECT{
    int x,y;
}myobject;

The above code creates an instance of OBJECT with the name of myobject. To create another instance of object you would need:

struct OBJECT myOtherObject;

To access a member variable of the structure you need to state which variable you're interested ie myOtherObject, myobject, and access the variable using the dot (.) notation or if you created a pointer use pointer notation (->). Ie. myOtherObject.x myobject.y.

typedef struct OBJECT{
  int x,y;
}MyNewObjectType;

The typedef creates a new Type, in the case above named MyNewObjectType, it doesn't create an instance of that Type, just names a new type. You can now create a new instance of this type without using the struct keyword.

struct OBJECT test; // Still valid but you must use the struct keyword to make an instance of this structure.
MyNewObjectType test1; // You don't need the struct keyword in this instance since MyNewObjectType is a Type of variable much like an int, or double.

Jim