在成员函数中使用shared_ptr作为私有变量C++

Question

我想在 class 的几个成员函数中重用 shared_ptr。

#include <iostream>
#include <memory>

class TestClass
{
    private:
        std::shared_ptr<int> int_shared_ptr;

    public:
        TestClass()
        {
            std::cout << "I will create a shared ptr object here.";
            std::shared_ptr<int> int_ptr (new int(10));
            std::shared_ptr<int> int_shared_ptr(int_ptr);
            std::cout << "The created shared ptr has value of " << *int_shared_ptr << "\n";

        }

        void check_if_shared()
        {
            std::cout << "The created shared ptr has value of " <<  int_shared_ptr << "\n";
        }

};


int main(){

    auto tc = TestClass();
    tc.check_if_shared();


}

输出

I will create a shared ptr object here.The created shared ptr has value of 10
The created shared ptr has value of 0

int_shared_ptr 一旦离开构造函数似乎就被破坏了。谁能建议一种在离开构造函数后保留共享指针的方法？

Answer 1

行

std::shared_ptr<int> int_shared_ptr(int_ptr);

创建一个与成员变量同名的函数局部变量。成员变量保持默认初始化。使用：

TestClass() : int_shared_ptr(new int(10))
{
    std::cout << "The created shared ptr has value of " << *int_shared_ptr << "\n";
}

使用std::make_shared更符合习惯：

TestClass() : int_shared_ptr(std::make_shared<int>(10))
{
    std::cout << "The created shared ptr has value of " << *int_shared_ptr << "\n";
}

Answer 2

所以我认为您正在尝试使用多个共享指针（实例成员）保存对同一个 int 的引用。这个简单的解决方案怎么样：

#include <memory>

class TestClass
{
    private:
        // you can have any number of shared pointers here

        std::shared_ptr<int> shared_0;
        std::shared_ptr<int> shared_1;
        std::shared_ptr<int> shared_2;

    public:
        TestClass()
        {
            // create new int once
            shared_0 = std::make_shared<int>(10);

            // copy references only
            shared_1 = shared_0;
            shared_2 = shared_0;

            std::cout << "shared_0: " << *shared_0 
                << "\nshared_1: " << *shared_1 
                << "\nshared_2: " << *shared_2 << "\n";
        }

        void check_if_shared()
        {
            std::cout << "shared_0: " << *shared_0 
                << "\nshared_1: " << *shared_1 
                << "\nshared_2: " << *shared_2 << "\n";
        }
};

int main()
{
    auto tc = TestClass();
    tc.check_if_shared();

    // now all shared pointers point to the same int
}

输出：

shared_0: 10
shared_1: 10
shared_2: 10
shared_0: 10
shared_1: 10
shared_2: 10

在成员函数中使用shared_ptr作为私有变量C++

Use shared_ptr among member functions as private variable C++

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