smart-pointers-2.md

Smart Pointers II — shared_ptr

• shared_ptr is a smart pointer with shared ownership, allowing multiple pointer instances to jointly own and manage the same object. It supports reference counting and automatic memory management.
• The key difference between ordinary references and rvalue references is that the latter "hints" that resources may be "stolen" (though no actual move occurs in this program). Summary:

Feature	Ordinary Reference (&)	Rvalue Reference (&&)
Accepts	Lvalues (variables)	Rvalues (temporaries, std::move results)
Call syntax	func(var)	func(std::move(var)) or func(temp_obj)
Reference count	Unchanged	Unchanged
Semantic meaning	Borrowed use	Preparing to transfer ownership
Source state	Unchanged	May be "moved from" (depends on impl)

• make_shared is a template function for creating shared_ptr. Compared to the traditional approach (std::shared_ptr<int> ptr(new int(42));), it is more memory-efficient and exception-safe. Summary:

Feature	make_shared	shared_ptr(new T)
Memory efficiency	High (single alloc)	Low (two allocs)
Exception safety	Yes	Potentially unsafe
Code brevity	Yes	More verbose
Custom deleter	Not supported	Supported
Memory release	May be delayed	Timely

• Differences between shared_ptr, unique_ptr, and weak_ptr:

Feature	shared_ptr	unique_ptr	weak_ptr
Ownership	Shared	Exclusive	Non-owning
Copyable	Yes	No	Yes
Reference count	Yes	No	Does not increment
Performance	Higher	Very low	Low