Moving temporary object prevents copy elision

1. What is guaranteed copy elision?
2. What is move elision?
3. How do you prevent RVO?
4. Does std :: move make a copy?
5. Does C have RVO?
6. What is NRVO?
7. What is the default move constructor?
8. Is NRVO guaranteed?
9. What is C++ move semantics?
10. How can you tell the difference between ischemic and nonischemic CRVO?
11. How many injections do you need for RVO?
12. What causes BRVO?
13. Is std :: move safe?
14. Does std :: move Delete?
15. When should you not use STD move?

What is guaranteed copy elision?

Guaranteed copy elision redefines a number of C++ concepts, such that certain circumstances where copies/moves could be elided don't actually provoke a copy/move at all. The compiler isn't eliding a copy; the standard says that no such copying could ever happen.

What is move elision?

Interaction between Move Semantic and Copy Elision in C++ ... Copy elision is the general process where, when returned from a function, an object is not copied nor moved, resulting in zero-copy pass-by-value semantics. It includes both return value optimization (RVO) and named return value optimization (NRVO).

How do you prevent RVO?

Prevention. Usually, an underlying medical condition brings on a retinal vein occlusion. So it's important to keep your blood pressure, cholesterol, and blood sugar under control. If you have diabetes, get your eyes checked every year.

Does std :: move make a copy?

8 Answers. In C++11, in addition to copy constructors, objects can have move constructors. (And in addition to copy assignment operators, they have move assignment operators.) ... std::move() is a cast that produces an rvalue-reference to an object, to enable moving from it.

Does C have RVO?

> Note also that C doesn't have return-value-optimization, hence all your struct-returning functions will cause a call to memcpy (won't happen when compiled in C++ mode of course). What ? RVO is precisely needed because a copy in C++ can run arbitrary code and so is not as easy to ellide as a memcpy.

What is NRVO?

RVO is stands for "return value optimization" and NRVO for "named return value optimization". What does all this staff mean? Typically, when a function returns an instance of an object, a temporary object is created and copied to the target object via the copy constructor.

What is the default move constructor?

Implicitly-defined move constructor

For non-union class types (class and struct), the move constructor performs full member-wise move of the object's bases and non-static members, in their initialization order, using direct initialization with an xvalue argument.

Is NRVO guaranteed?

Compilers often perform Named Return Value Optimization (NRVO) in such cases, but it is not guaranteed.

What is C++ move semantics?

Move semantics is about transferring resources rather than copying them when nobody needs the source value anymore. In C++03, objects are often copied, only to be destroyed or assigned-over before any code uses the value again.

How can you tell the difference between ischemic and nonischemic CRVO?

Presentation is with sudden, unilateral blurred vision. In non-ischemic CRVO, the blurring is mild and may be worse on waking and improves during the day. In ischemic CRVO, visual impairment is sudden and severe.

How many injections do you need for RVO?

Lucentis and Eylea are licensed for use in vein occlusion patients and have been extensively studied in research clinic trials. The effect of Lucentis and Eylea is temporary so they must be given repeatedly over a year or more. Patients receive 4 injections, 1 injection every month, as an automatic loading dose.

What causes BRVO?

Retinal vein occlusion happens when a blood clot blocks the vein. Sometimes it happens because the veins of the eye are too narrow. It is more likely to occur in people with diabetes, and possibly high blood pressure, high cholesterol levels, or other health problems that affect blood flow.

Is std :: move safe?

tl;dr: Yes, this is safe, for several reasons.

std::move is a cast to an rvalue-reference, which primarily changes which constructor/assignment operator overload is chosen. In your example the move-constructor is the default generated move-constructor, which just copies the ints over so nothing happens.

Does std :: move Delete?

For every new, there's a delete. If you don't want to delete it yourself, consider std::unique_ptr , which is aware about move semantics. Built-in type such as raw pointer, int, floats are not aware of move semantics and moving them will simply copying them.

When should you not use STD move?

Don't use std::move in a return statement. Trust your optimiser! If you return the object just by copy, the optimiser will do its job. This is best practices until C++14; this is an obligatory rule since C++17 and is called guaranteed copy elision.