Get object from pointer C++

Question

I have a vector of objects (DimensionItem) and I want to push another item to the vector. I only have a pointer to the object I wish to push. How can I get the object from the pointer.

(New to pointers, very possible I'm am fundamentally misunderstanding something)

DimensionItem *selected_Item = dynamic_cast<DimensionItem*>(g_items[i]); //g_items is a list of items taken from my scene

vector<DimensionItem> DimItems;
DimItems.push_back(selected_Item);

The error message is:

no matching function for call to 'std::vector::push_back(DimensionItem*&)'

If `selected_Item` is a pointer, you cannot add it to the container of objects. Instead, you must dereference the pointer with `*` operator. — vahancho, Jun 14 '19 at 11:56
Reopened because there is more than just dereferencing to this question. — Maxim Egorushkin, Jun 14 '19 at 19:48

Maxim Egorushkin · Answer 1 · 2019-06-14T11:59:52.273

3

You probably want:

DimensionItem& selected_Item = dynamic_cast<DimensionItem&>(*g_items[i]); // Throws if g_items[i] is not DimensionItem.
vector<DimensionItem> DimItems;
DimItems.push_back(selected_Item); // Stores a copy of selected_Item.

dynamic_cast<DimensionItem*>(g_items[i]) returns a null pointer if g_items[i] is not a DimensionItem, so the code would need to check the pointer for null before dereferencing it.

Whereas dynamic_cast<DimensionItem&>(*g_items[i]) throws an exception in that case.

edited Jun 14 '19 at 11:59

answered Jun 14 '19 at 11:56

Maxim Egorushkin

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Since OP seems to be new to pointers, you should probably mention, that your code will create copy of original value. – Radosław Cybulski Jun 14 '19 at 11:59
@RadosławCybulski Done. – Maxim Egorushkin Jun 14 '19 at 11:59

Get object from pointer C++

1 Answers1