Difference between - and . for accessing members in C++
Author
I've been trying to figure that out for a while, have been looking around the web for answers and all. Coming from a programming background with languages where you either have -> or . to access members it was rather confusing for me to see that in C++ you have both. And in thinking about it and trying to find out when to use which I am only getting more confused... So, I'd greatly welcome any help any of you might be able to give me.
Okay, so from what I understand you can use . to access members of structs and object and call methods of objects. But when you have a pointer to the object/struct you use -> instead. However when I started thinking about that, I came to believe that I must have misunderstood. When you create an instance of an object what you have in that variable that holds the instance is actually a reference to where the information of that object is saved, isn't it? And isn't a reference kind of the same as a pointer? That would then mean that I would never use . and always -> which definately isn't true...
I think it is safe to say that I am utterly and hopelessly confused about this. I am sure it is a rather simple matter but I have this weird talent for getting the simplest concepts totally distorted and knoted up in my head... [rolleyes]
-> and . do almost the same thing, but -> requires a pointer type as its left argument, and . requires a reference type.
Thus, you can do this:
That's really all there is to it (unless you want to go into operator overloading).
Thus, you can do this:
struct Point { float x; float y;};float foo( Point a, Point * pb ) { return a.x + pb->x + (&a)->y + (*pb).y;}That's really all there is to it (unless you want to go into operator overloading).
Simple one this. The . operator is used to access members of a class/struct and the -> operator is used to access members of a class/struct via a pointer.
Example:
Barring any syntax errors that should compile and run, setting the x member of foo and pFoo to 7.
-hellz
Example:
class CFoo{public: int x, y; CFoo(int x, int y) { this->x = x, this->y = y; }};int main(){ CFoo foo(5, 6); CFoo *pFoo = new CFoo(5, 6); foo.x = 7; pFoo->x = 7; delete pFoo; // Remember to match each use of new with a delete. return 0;}Barring any syntax errors that should compile and run, setting the x member of foo and pFoo to 7.
-hellz
Quote:Original post by hplus0603
-> and . do almost the same thing, but -> requires a pointer type as its left argument, and . requires a reference type.
Thus, you can do this:struct Point { float x; float y;};float foo( Point a, Point * pb ) { return a.x + pb->x + (&a)->y + (*pb).y;}
That's really all there is to it (unless you want to go into operator overloading).
Cool. I didn't know you could do (&Object)->; Hehe.
Quote:Original post by Pipo DeClown
pObject->foo
equals
(*pObject).foo
Yeah -> is actually "syntactic sugar".Less writing
Author
Ah, thank you! So, my actual problem was in seeing that there is a difference between a reference and a pointer... Hehe, sometimes I feel really dense. Ah, well. In order to learn one needs to make mistakes. [smile]
And again, thank you. As always, you people have been very helpful.
And again, thank you. As always, you people have been very helpful.
(Adding stuff to what has been said)
The C++ -> operator can be overloaded (this is actually damn cool because it allow you to use smart pointers transparently), while . cannot.
The C++ -> operator can be overloaded (this is actually damn cool because it allow you to use smart pointers transparently), while . cannot.
Main use of pointers (as i see it at least) are to "update" stuff. For example, use a pointer to update the data stored in an array:
type *object = &array[2];
object->x = 2;
object->y = 2;
compared too:
type object = array[2];
object.x = 2;
object.y = 2;
array[2] = object;
(just adding that for someone wondering the use of pointers)
type *object = &array[2];
object->x = 2;
object->y = 2;
compared too:
type object = array[2];
object.x = 2;
object.y = 2;
array[2] = object;
(just adding that for someone wondering the use of pointers)
Quote:Original post by Interesting Dave
Main use of pointers (as i see it at least) are to "update" stuff. For example, use a pointer to update the data stored in an array:
type *object = &array[2];
object->x = 2;
object->y = 2;
compared too:
type object = array[2];
object.x = 2;
object.y = 2;
array[2] = object;
(just adding that for someone wondering the use of pointers)
compared too:type object = &array[2]; //I don't know if this compiles, it shouldobject.x = 2;object.y = 2;//array[2] = object; //No needThis topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
