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

c++ c++11 auto
lurscher picture lurscher · Jan 10, 2012 · Viewed 10.1k times · Source

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?

Answer

R. Martinho Fernandes picture R. Martinho Fernandes · Jan 10, 2012

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*.

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