将现有值分配给smart-ptrs? [英] Assigning existing values to smart-ptrs?

问题描述

我只是在学习智能指针，而在将变量的现有位置分配给标准库的共享指针时遇到了麻烦.

I am just learning about smart pointers, and I am having trouble assigning a pre-existing location of a variable to the standard library's shared pointer.

例如，假设您有一个不知道其值的int x.使用普通的指针，我就做到了

For example, lets say you have an int x, which you do not know the value of. With normal pointers, I just did

int* ptr;
ptr = &x;

我尝试了使用共享指针的尝试，

I tried both that with shared pointers, and

std::tr1::shared_ptr<int> ptr;
ptr = std::make_shared<int> (&x)

所以我对如何做到这一点很迷茫.

So i'm fairly lost as to how to do it.

推荐答案

您通常不会(但通常)将智能指针指向现有变量.智能指针管理动态分配对象的生命周期，使用后将其删除；如果将其指向未动态分配的内容，则尝试删除它会导致错误.

You wouldn't (usually) make a smart pointer point to an existing variable. A smart pointer manages the lifetime of a dynamically allocated object, deleting it after use; pointing it to something that wasn't dynamically allocated will cause an error if it tries to delete it.

通常将使用new或make_shared创建对象，并使用以下结果创建或分配智能指针:

You would usually use new or make_shared to create an object, and create or assign a smart pointer with the result of that:

std::shared_ptr<int> ptr(new int(42)); // Create a new pointer to manage an object
ptr.reset(new int(66));                // Reset to manage a different object
ptr = std::make_shared<int>(53);       // Use `make_shared` rather than `new`

make_shared通常比new更可取，因为它可以更好地利用内存并提供更强的异常安全性.

make_shared is usually preferable to new, since it makes better use of memory and gives stronger exception-safety.

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