What is std::move(), and when should it be used and does it actually move anything?

1. “What is it?” While std::move() is technically a function – I would say it isn’t really a function. It’s sort of a converter between ways the compiler considers an expression’s value. 2. “What does it do?” The first thing to note is that std::move() doesn’t actually move anything. It changes an expression from being … Read more

Is std::array movable?

std::array is movable only if its contained objects are movable. std::array is quite different from the other containers because the container object contains the storage, not just pointers into the heap. Moving a std::vector only copies some pointers, and the contained objects are none the wiser. Yes, std::array uses the default move constructor and assignment … Read more

Move constructor on derived object

rval is not a Rvalue. It is an Lvalue inside the body of the move constructor. That’s why we have to explicitly invoke std::move. Refer this. The important note is Note above that the argument x is treated as an lvalue internal to the move functions, even though it is declared as an rvalue reference … Read more

problems with Move constructor and Move overloaded assignment operator?

Your class A has several issues: Your assignment operator don’t handle self assignment and leak: A& A::operator=(const A& a) { std::cout<<“overload operator=\n”; if (this != &a) { p = a.p; delete[] s; s = new char[strlen(a.s) + 1]; strcpy(s, a.s); } return *this; } Your move doesn’t move but copy: A::A(A&& a) : p(a.p), s(a.s) … Read more

Should I delete the move constructor and the move assignment of a smart pointer?

Guideline Never delete the special move members. In typical code (such as in your question), there are two motivations to delete the move members. One of those motivations produces incorrect code (as in your example), and for the other motivation the deletion of the move members is redundant (does no harm nor good). If you … Read more

copy vs std::move for ints

In this example, there is no difference. We will end up with 3 ints with value 100. There could definitely be a difference with different types though. For instance, let’s consider something like vector<int>: std::vector<int> a = {1, 2, 3, 4, 5}; // a has size 5 auto a_copy = a; // copy a. now … Read more

Can I typically/always use std::forward instead of std::move?

The two are very different and complementary tools. std::move deduces the argument and unconditionally creates an rvalue expression. This makes sense to apply to an actual object or variable. std::forward takes a mandatory template argument (you must specify this!) and magically creates an lvalue or an rvalue expression depending on what the type was (by … Read more

Is it possible to std::move objects out of functions? (C++11)

Given this example, X foo () { X x; return x; } the following behavior is guaranteed: • If X has an accessible copy or move constructor, the compiler may choose to elide the copy. This is the so-called (named) return value optimization ((N)RVO), which was specified even before C++11 and is supported by most … Read more

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