shared_ PTR and make_ Use of shared

 std::shared_ptr

It's a kind of Intelligent pointer （ Itself is an object ）, Point to an object . It can record how many shared_ptr Point to an object together , This eliminates the displayed call delete, When the reference count becomes zero, the object is automatically deleted .

std::shared_ptr Can pass get() Method to get the original pointer , adopt reset() To reduce a reference count , And pass use_count() To see the reference count of an object .

// Created a  40 Byte memory space   The object of ,pointer  Point to this object 
std::shared_ptr pointer = new int(10);     
std::shared_ptr pointer2 = pointer; // pointer2   And point to this object , And reference count +1

int *p = pointer.get(); //  This does not increase the reference count 
std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl; // 3
std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl; // 3


// Create a pointer ptrB  Stack object , There are no arguments in the constructor , So the default point is null.
std::shared_ptr<int> ptrB();
 
// This kind of writing can also ,{} It means to assign initial value or initialize , The same is true for other types of variable definitions , yes c++11 Syntax features of 
std::shared_ptr<int> ptrB{std::make_shared<int>(5)};

Be careful ：std::make_shared Arrays are not supported .

std::make_shared

The main function is to allocate an object in dynamic memory and initialize it , Returns... Pointing to this object shared_ptr.

//p1 Point to a value of "9999999999" Of string object 
shared_ptr<string> p1 = make_shared<string>(10, '9');

//p2 Point to a value of "hello" Of string object 
shared_ptr<string> p2 = make_shared<string>("hello");

//p2 Point to an empty string object 
shared_ptr<string> p3 = make_shared<string>();

// This kind of writing can also ,{} It means to assign initial value or initialize , The same is true for other types of variable definitions , yes c++11 Syntax features of 
std::shared_ptr<int> ptrB{std::make_shared<int>(5)};

Use directly with the above new<string>("hello") comparison , What are the benefits ：

Look at the next two pictures ： Memory allocation can be completed at one time . This reduces the number of memory allocations , Memory allocation is a costly operation .

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Reference article ：

std::shared_ptr Use _lyshiba The blog of -CSDN Blog _shared_ptr Use

std::make_shared_zhgeliang The blog of -CSDN Blog _std::make_shared

std::shared_ptr - Simple books