c++ object array + argument with reference and pointer

Question

I don't understand the 2nd argument. Whats is it exactly? And most importantly he(the programmer) uses it to create a new array of Object objects , of num (the variable) size at the end.

void expand(const Object &s, Object* &children, int &num)
{
   ...
   children = new Object[num]; // <----
}

I would suggest you read a [good C++ book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). It is, obviously, a reference to a pointer to `Object`. What's unclear about that? — Algirdas Preidžius, Mar 17 '17 at 20:30
It is ugly, but you can use the [Clockwise/Spiral Rule](http://c-faq.com/decl/spiral.anderson.html) to decipher most C and C++ declarations. — Rama, Mar 17 '17 at 20:33
Algirdas Preidžius: So the function takes as a 2nd argument the MEMORY ADDRESS of the pointer named children , which points to type Object? — DIMITRIOS, Mar 17 '17 at 20:39
@DIMITRIOS That's why I suggested reading a C++ book. Reference != memory address. Probably you are confusing references, and address-of operator? — Algirdas Preidžius, Mar 17 '17 at 20:40
See [this answer](http://stackoverflow.com/questions/3834067/c-difference-between-and-in-parameter-passing) for some explanations on `*&` (as well as `**`). — ssell, Mar 17 '17 at 21:01
@DIMITRIOS I updated your question, focusing on the gist of it, hope you don't mind. Don't forget to *accept* an answer BTW! — gsamaras, Mar 17 '17 at 21:01

score 2 · Answer 1 · edited Mar 17 '17 at 21:02

2

Read it from right to left:

When you reach a *, replace it by pointer to.
When you reach a &, replace it by reference of.

So children will be: A reference of a pointer to an Object.

edited Mar 17 '17 at 21:02

gsamaras

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answered Mar 17 '17 at 20:39

Rama

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I like your answer, but I posted a new one, to augment the answer's section. Nice! – gsamaras Mar 17 '17 at 20:58

score 1 · Answer 2 · answered Mar 17 '17 at 20:50

Second argument: Object* &children Object* says that children is a pointer to Object type. & prevent from receiving a copy of children from calling scope and lets us to work directly with argument variable, so when you change children :

children = new Object[num];

you change the argument variable in calling scope and after expand function returns, you have access to:

new Object[num]

via the argument variable that you passed to expand function.

Passing arguments by reference, is another way to receive information from function (It has other usages too).

score 1 · Answer 3 · answered Mar 17 '17 at 20:55

1

It's:

a reference of a pointer to an Object

The reason is that because it allocates dynamically memory, he probably wants this change to children to be reflected in the caller of the function (probably main()).

answered Mar 17 '17 at 20:55

gsamaras

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c++ object array + argument with reference and pointer

3 Answers3