std::make_shared

Object-Generator idiom

make_shard使用的是Object-Generator idiom，参见C++\Idiom\Template-metaprogramming\Object-Generator。

Prefer std::make_shared over new expression

在下面文章中，对此进行了说明:

1、stackoverflow is it better to use shared_ptr.reset or operator =?

2、

cppreference std::make_shared

Example

Example1 make_shard with no argument

这个例子是源自cppreference std::make_shared, std::make_shared_for_overwrite

#include <iostream>
#include <memory>
#include <type_traits>

struct C
{

  int i;
};

int main()
{
    auto sp = std::make_shared<C>();

    //static_assert(std::is_same_v<decltype(sp), std::shared_ptr<C>>);

    std::cout << sp->i << '\n';
}

Example2

这个例子源自learncpp 15.6 — std::shared_ptr：

#include <iostream>
#include <memory> // for std::shared_ptr

class Resource
{
public:
    Resource() { std::cout << "Resource acquired\n"; }
    ~Resource() { std::cout << "Resource destroyed\n"; }
};

int main()
{
    // allocate a Resource object and have it owned by std::shared_ptr
    auto ptr1 = std::make_shared<Resource>();
    {
        auto ptr2 = ptr1; // create ptr2 using copy initialization of ptr1

        std::cout << "Killing one shared pointer\n";
    } // ptr2 goes out of scope here, but nothing happens

    std::cout << "Killing another shared pointer\n";

    return 0;
} // ptr1 goes out of scope here, and the allocated Resource is destroyed