CODEWITHSUNDEEP
c++c++11auto
lurscher
lurscher

Reputation: 26973

auto from const std::vector<>&; object or reference?

suppose we have an object with the following interface:

struct Node_t {
 ... const std::vector< something >& getChilds() const;
 } node;

Now, i access the property with an auto variable like this:

auto childs = node->getChilds();

what is the type of childs? a std::vector< something > or a reference to one?

Upvotes: 21

Views: 10386

Answers (3)

R. Martinho Fernandes
R. Martinho Fernandes

Reputation: 234584

The type of childs will be std::vector<something>.

auto is powered by the same rules as template type deduction. The type picked here is the same that would get picked for template <typename T> f(T t); in a call like f(node->getChilds()).

Similarly, auto& would get you the same type that would get picked by template <typename T> f(T& t);, and auto&& would get you the same type that would get picked by template <typename T> f(T&& t);.

The same applies for all other combinations, like auto const& or auto*.

Upvotes: 24

lapk
lapk

Reputation: 3918

auto gives you std::vector<something>. You can either specify reference qualifier auto & or, alternatively, you can use decltype:

decltype( node->getChilds() ) childs = node->getChilds();

Upvotes: 3

Benjamin Lindley
Benjamin Lindley

Reputation: 103733

It's an std::vector<something>. If you want a reference, you can do this:

auto & childs = node->getChilds();

That will of course be a const reference.

Upvotes: 21

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