Accessing element from reference to vector of pointers

Question

I have a reference to a vector of pointers, as follows:

std::vector<Object*>& objects;

How can I access Objects from this vector?

`objects` being a reference is irrelevant, you access it the same way as a non reference vector. — , Jan 03 '21 at 19:31
@πάνταῥεῖ I am afraid that gives me a "expression must have class type" error (I am using Visual Studio '19) — Con O'Leary, Jan 03 '21 at 19:42
@ConÓg I can't tell, since you're not really showing us what you're actually doing. Hard to tell what went wrong with something you can't even see. — πάντα ῥεῖ, Jan 03 '21 at 19:45
@πάνταῥεῖ I understand. My thinking is to exclude as much code as possible in questions to reduce reading, so I hope I didn't exclude anything important. Getting a reference for the Object I want, Object *o = objects[i]; , and then proceeding to use the indirect access operator, -> , on my new pointer seems to work — Con O'Leary, Jan 03 '21 at 20:00
@ConÓg You excluded almost everything imprtant in your question. Are you kidding me? — πάντα ῥεῖ, Jan 03 '21 at 20:02
@πάνταῥεῖ I can't imagine how what further plans I have for this hypothetical object have bearing on a question relating to accessing it — Con O'Leary, Jan 03 '21 at 20:11
@πάνταῥεῖ Shouldn't that have been `(*objects[index_you_want]).doObjectFunc();`? — Daniel Langr, Jan 03 '21 at 20:40

vmp · Answer 1 · 2021-01-03T20:07:56.010

1

You can index it with [] as long as you don't try to access an elment outside the the vector... or to be safer, if you need to do something to every element you could use a range based for loop:

for(auto& object : objects) 
   object->someFunction();

edited Jan 03 '21 at 20:07

answered Jan 03 '21 at 19:31

vmp

2,370
1
13
17

1

Since `object` is an `Object*`, it'd need to be `object->someFunction();`. – Eljay Jan 03 '21 at 19:34
Yep, that works once I use "->" – Con O'Leary Jan 03 '21 at 19:45
@Eljay Well noticed, I've edited – vmp Jan 03 '21 at 20:08

score 1 · Accepted Answer · answered Jan 03 '21 at 19:34

That objects is a reference has no direct bearing on the question -- you use a reference in exactly the same way you use a simple identifier for the same object.

Thus, you can select an individual element of the vector by any of the normal means, such as by index, by iterator, or whatever. The result is of the vector's element type, which is Object *:

Object *o = objects[42];

You can access the object to which o points via the dereference operator (unary *). Alternatively, you can use the indirect access operator (->) to access its methods and fields:

(*o).do_something();
int i = o->an_int;

I understand why your solution works. Thank you John – Con O'Leary Jan 03 '21 at 19:50 — Con O'Leary, Jan 03 '21 at 19:50

Accessing element from reference to vector of pointers

2 Answers2