How does return value optimization work?

In the context of the C++ programming language, return value optimization (RVO) is a compiler optimization that involves eliminating the temporary object created to hold a function’s return value. RVO is allowed to change the observable behaviour of the resulting program by the C++ standard.

What is return object optimization?

RVO is a compiler technique to avoid copying objects when the object is returned as function value. This optimization helps a function to efficiently return large objects while also simplifying the function’s interface and eliminating scope for errors.

Does C have return value optimization?

> 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).

Is std :: move necessary?

std::move itself does “nothing” – it has zero side effects. It just signals to the compiler that the programmer doesn’t care what happens to that object any more. i.e. it gives permission to other parts of the software to move from the object, but it doesn’t require that it be moved.

What is named return value optimization?

(Named) Return value optimization is a common form of copy elision. It refers to the situation where an object returned by value from a method has its copy elided. The example set forth in the standard illustrates named return value optimization, since the object is named.

Is NRVO guaranteed?

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

Is move faster than reference?

Consider reading this question and answers. Moving is an optimization of copy (for xvalues), not of passing by reference. Of course passing a simple reference is faster.

Is std :: move faster than copy?

It’s faster because moving allows the source to be left in a invalid state, so you can steal it’s resources. For example, if a object holds a pointer to a large block of allocated memory, a move can simply steal the pointer while a copy must allocate its own memory and copy the whole memory block.

Is return value optimization guaranteed?

What is NRVO?

This post describes these optimizations and shows how to benefit from them in your code. There are 2 optimizations related to return value: the RVO (Return Value Optimization), the NRVO (Named Return Value Optimization)

Should I always use std move?

Q: When should it be used? A: You should use std::move if you want to call functions that support move semantics with an argument which is not an rvalue (temporary expression).

Do I need to return std :: move?

std::move is totally unnecessary when returning from a function, and really gets into the realm of you — the programmer — trying to babysit things that you should leave to the compiler.