In C++, the std::shared_ptr is a smart pointer that allows multiple owners to share ownership of an object. It’s commonly used to manage resources and automatically deallocate them when they’re no longer needed.

Sometimes, we come across scenarios where we need to obtain a shared_ptr from a raw pointer within the object itself. This is where the std::enable_shared_from_this class template comes into play.

What is std::enable_shared_from_this?

std::enable_shared_from_this is a base class template provided by the C++ Standard Library. It allows an object to create a shared_ptr that shares ownership with other shared_ptr instances that already exist.

Usage Example

Let’s say we have a class MyClass that needs to obtain a shared_ptr of itself. Here’s how we can use std::enable_shared_from_this to accomplish this:

#include <iostream>
#include <memory>

class MyClass : public std::enable_shared_from_this<MyClass> {
public:
    void doSomething() {
        std::shared_ptr<MyClass> sharedPtr = shared_from_this();

        // Use sharedPtr here
    }
};

int main() {
    std::shared_ptr<MyClass> obj = std::make_shared<MyClass>();
    obj->doSomething();

    return 0;
}

In this example, MyClass publicly inherits from std::enable_shared_from_this<MyClass>, enabling it to create a shared_ptr using the shared_from_this() member function. Inside the doSomething() member function, we can obtain a shared_ptr of the current object by calling shared_from_this().

It’s important to note that in order to use shared_from_this(), the object should already have been assigned to a shared_ptr. In the example, we create a shared_ptr using std::make_shared<MyClass>(), which allows us to call doSomething() and obtain a valid shared_ptr of the object.

Advantages and Considerations

Using std::enable_shared_from_this with std::shared_ptr provides the following advantages:

• Simplifies the creation of shared_ptr instances for objects.
• Allows objects to internally obtain shared_ptr instances, ensuring proper reference counting and avoiding double deletion.

However, there are some considerations to keep in mind:

• An object should only inherit from std::enable_shared_from_this if it’s intended to be used with shared_ptr.
• #C++ The inheritance should always be public. Declaring it as private or protected will result in compilation errors.

By leveraging std::enable_shared_from_this and std::shared_ptr, you can easily manage object lifetimes and safely share ownership among multiple instances in C++. #C++ #SmartPointer