Final answer:
Marking the move constructor as noexcept in C++ is essential for performance optimization, as it allows move operations in containers without risking exception safety.
Step-by-step explanation:
It is necessary to mark the move constructor as noexcept in C++ because it allows the compiler to make certain optimizations, especially when objects are being moved instead of copied during resizing operations in containers like std::vector.
If the move constructor is not noexcept, the container may choose to use the copy constructor instead to prevent the strong exception guarantee from being violated in case the move operation throws an exception.
This can lead to poor performance because copying is usually more expensive than moving.
By marking the move constructor as noexcept, you tell the compiler that the move operation will not throw any exceptions, enabling it to use moves even in contexts where exception safety is paramount.