Smart Pointers
Good video: https://youtu.be/UOB7-B2MfwA
Their purpose is only to create new objects and not to point to existing objects
Please refer to the code examples which also include comments for better understanding:
Unique pointers
https://en.cppreference.com/w/cpp/memory/unique_ptr/
Creates new object, and gives a unique pointer to that object
Smart Pointer entirely owns the object
object is deleted when the unique pointer is out of scope
Copy Constructor and operator of unique_ptr is explicitly deleted
must use move symantics, if
- need to pass to a function / constructor
- need to create annother unique pointer but pointing to same object
https://en.cppreference.com/w/cpp/memory/unique_ptr/make_unique
Use make_unique to create the object in a safer way (error handling while constructing), then pass it to unique_ptr
Else we can also directly pass new Object() in the constructor of unique_ptr, might create dangling pointer if constructor of object threw some error
Shared pointers
https://en.cppreference.com/w/cpp/memory/shared_ptr
Creates new object, and gives a pointer to that object
Pointer can be copied to another pointer
Pointer can be passed to a function / constructor with copy symantics
The shared_ptr keeps track of how many total pointer point to the same data
object is deleted when all the pointers are out of scope
https://en.cppreference.com/w/cpp/memory/shared_ptr/make_shared
Must use make_shared to generate object and pass it to shared_ptr constructor
Weak Pointer
https://en.cppreference.com/w/cpp/memory/weak_ptr
Points to a already defined shared_ptr
But does not increase pointer count of shared_ptr
So its possible, that weak_ptr is pointing to an object that is deleted since all its shared_ptr were out of scope
In such case, we must first check if weak_ptr is valid using provided methods
About make_shared and make_unique
make_unique<T>(args) and make_shared<T>(args) pass the “args” to one of the valid constructors of type T.
They will always create a new object which the smart pointer owns.
even if you pass an existing object, they will either call “copy constructor” or “move constructor”.
But they will not point to existing object.