What is a smart pointer 、 effect

Smart pointers are used to ensure that objects can be automatically deleted when they are no longer in use .

std::shared_ptr

Several pointers can point to the same object in a shared way , When there is no pointer to this object , The object is deleted （ destructor ）.

// std::shared_ptr<MyTime> mt0 = new MyTime(0, 70); // error  Type mismatch 
// MyTime* mt0 = std::make_shared(1, 70); // error  Type mismatch 
std::shared_ptr<MyTime> mt1(new MyTime(10));
std::shared_ptr<MyTime> mt2 = mt1; // mt2 and mt1 Point to the same object 

auto mt1 = std::make_shared<MyTime>(1, 70); // C++17

std::unique_ptr

And std::shared_ptr Different , One std::unique_ptr Will point to an object and no other pointers are allowed to point to .

std::unique_ptr<MyTime> mt1(new MyTime(10));
std::unique_ptr<MyTime> mt2 = std::make_unique<MyTime>(80); // C++17

however , One being std::unique_ptr The object pointed to can be move To another pointer pointing to .

std::unique_ptr<MyTime> mt3 = std::move(mt1);

How to understand smart pointers

The type of smart pointer is essentially a template class , So smart pointers are objects , With life cycle , At the end of the life cycle , The smart pointer destroys the call destructor .
for example ：std::shared_ptr The destructor of will reduce the number of pointers to the object 1, When there is no pointer to the object , Object memory destroyed .