std::move (3) - Linux Manuals
Defined in header <utility>
template< class T > (since C++11)
typename std::remove_reference<T>::type&& move( T&& t ) noexcept; (until C++14)
template< class T > (since C++14)
constexpr typename std::remove_reference<T>::type&& move( T&& t ) noexcept;
std::move is used to indicate that an object t may be "moved from", i.e. allowing the efficient transfer of resources from t to another object.
In particular, std::move produces an xvalue_expression that identifies its argument t. It is exactly equivalent to a static_cast to an rvalue reference type.
t - the object to be moved
The functions that accept rvalue reference parameters (including move_constructors, move_assignment_operators, and regular member functions such as std::vector::push_back) are selected, by overload_resolution, when called with rvalue arguments (either prvalues such as a temporary objects or xvalues such as the one produced by std::move). If the argument identifies a resource-owning object, these overloads have the option, but aren't required, to move any resources held by the argument. For example, a move constructor of a linked list might copy the pointer to the head of the list and store nullptr in the argument instead of allocating and copying individual nodes.
Names of rvalue_reference variables are lvalues and have to be converted to xvalues to be bound to the function overloads that accept rvalue reference parameters, which is why move_constructors and move_assignment_operators typically use std::move:
One exception is when the type of the function parameter is rvalue reference to type template parameter ("forwarding reference" or "universal reference"), in which case std::forward is used instead.
Unless otherwise specified, all standard library objects that have been moved from are placed in a valid but unspecified state. That is, only the functions without preconditions, such as the assignment operator, can be safely used on the object after it was moved from:
Also, the standard library functions called with xvalue arguments may assume the argument is the only reference to the object; if it was constructed from an lvalue with std::move, no aliasing checks are made. In particular, this means that standard library move assignment operators do not have to perform self-assignment checks:
// Run this code
forward forwards a function argument
move_if_noexcept obtains an rvalue reference if the move constructor does not throw
move moves a range of elements to a new location