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Questions tagged [rvalue-reference]

An rvalue reference is a new language feature in C++11 representing a reference to an rvalue. Together with reference collapsing, they are used to implement and enable move semantics and perfect forwarding.

An rvalue reference is a language feature added in C++11 (formerly known as C++0x). It is used to bind to an rvalue thus extending the temporary object's lifetime.

Together with reference collapsing, they are used to implement and enable move semantics and perfect forwarding.

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C++, rvalue references in function parameters

I'm trying to understand rvalue references. I have seen how they are used in constructors, with things like std::move and std::forward, but I still don't understand why this doesn't work: void func(string&& str) { cout << str << endl; } int…
CarlosHD
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C++0x rvalue references - lvalues-rvalue binding

This is a follow-on question to C++0x rvalue references and temporaries In the previous question, I asked how this code should work: void f(const std::string &); //less efficient void f(std::string &&); //more efficient void g(const char * arg) { …
Doug
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Why do we need to set rvalue reference to null in move constructor?

//code from https://skillsmatter.com/skillscasts/2188-move-semanticsperfect-forwarding-and-rvalue-references class Widget { public: Widget(Widget&& rhs) : pds(rhs.pds) // take source’s value { rhs.pds = nullptr; // why?? …
uchar
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Swapping with rvalues

Suppose I want swap that works on rvalues, and don't want to write 4 versions for all combinations of rvalue/lvalue references (rvalue/rvalue version is kinda pointless but it doesn't hurt). I came up with this: template
yuri kilochek
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Should I std::move a shared_ptr in a move constructor?

Consider: #include #include #include #include #include #include using namespace std; class Gizmo { public: Gizmo() : foo_(shared_ptr(new string("bar"))) {}; Gizmo(Gizmo&&…
John Dibling
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About catching exception good practices

I'm writing a little program in C++11 and really use exceptions for one of the first time. I've got a question about how to catch the exceptions efficiently, and after some googling I still don't have the answer. Here is the question : What is the…
Jaffa
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move constructor and std::move confusion

I am reading about the std::move, move constructor and move assignment operator. To be honest, all I got now is confusion. Now I have a class: class A{ public: int key; int value; A(){key = 3; value = 4;} //Simple move constructor …
Allanqunzi
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Return value or rvalue reference?

In Scott Meyer's new book, he proposes an example usage for rvalue reference qualifiers that looks something like this: class Widget { private: DataType values; public: DataType& data() & { return values; } DataType data() && {…
Barry
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Extending temporary's lifetime through rvalue data-member works with aggregate, but not with constructor, why?

I've found the following scheme to extend a temporaries lifetime works, I don't know if it should, but it does. struct S { std::vector&& vec; }; int main() { S s1{std::vector(5)}; // construct with temporary std::cout <<…
Ryan Haining
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construction helper make_XYZ allowing RVO and type deduction even if XZY has noncopy constraint

UPDATE1: C++17 added type deduction for constructors - which does not imply that the free function is an inferior solution. UPDATE2: C++17 added guaranteed copy elision (the copy does not even take place conceptually). So with C++17 my code actually…
Patrick Fromberg
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Should I write constructors using rvalues for std::string?

I have a simple class: class X { std::string S; X (const std::string& s) : S(s) { } }; I've read a bit about rvalues lately, and I've been wondering, if I should write constructor for X using rvalue, so I would be able do detect temporary…
Bartek Banachewicz
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Intuitive understanding of functions taking references of references

Possible Duplicate: What does T&& mean in C++11? For some reason, this is eluding my intuition, and I cannot find any explanation on the internet. What does it mean for a C++ function to take a reference of a reference? For example: void…
Daniel
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Why does operator* of rvalue unique_ptr return an lvalue?

Using the return value of operator* from a "dead" unique_ptr is bad. The following code compiles but results of course in Undefined Behavior: auto& ref = *std::make_unique(7); std::cout << ref << std::endl; Why didn't the standard make the…
Amir Kirsh
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Avoid dangling reference for reverse range-based for-loop implementation

Background and Previous Search I'm looking for an elegant way to reverse-iterate over a container (e.g. std::vector) using a range-based for-loop in C++14. Searching for a solution I found this Q/A. It basically tells me, that this is not part of…
Don-Umbro
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Classes, Rvalues and Rvalue References

An lvalue is a value bound to a definitive region of memory whereas an rvalue is an expression value whose existence is temporary and who does not necessarily refer to a definitive region of memory. Whenever an lvalue is used in a position in which…
No One
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