C++ Smart Pointers: Advanced Usage and Considerations

C Smart Pointers: Advanced Usage and Precautions

Advanced Usage:

1. Custom smart pointers:
You can create your own smart pointers, inherit from std::unique_ptr or std::shared_ptr, and customize the behavior for specific needs. .

class CustomPtr : public std::unique_ptr {
public:
    CustomPtr(int* ptr) : std::unique_ptr(ptr) {}
    ~CustomPtr() { std::cout << "CustomPtr destroyed" << std::endl; }
};

2. Convert smart pointers:
You can use the std::make_unique and std::make_shared functions to easily Convert between types of smart pointers.

std::unique_ptr up = std::make_unique(42);
std::shared_ptr sp = std::make_shared(*up);

3. Circular Reference:
When two smart pointers refer to each other, a circular reference may be created. You can change the type of one of the smart pointers to break the cycle.

struct Node {
    std::unique_ptr next;
    std::shared_ptr prev;
};

Notes:

1. Memory leak:
Forgetting to wrap resources with smart pointers can lead to memory leaks. Make sure to always use smart pointers to manage dynamically allocated memory.

2. Dangling pointers:
Smart pointers may point to deleted objects, resulting in dangling pointers. Avoid checking the validity of smart pointers before using them.

3. Self-looping:
Smart pointers can point to themselves, causing self-looping. Avoid allocating the same object in the constructor of a smart pointer.

4. Performance overhead:
Smart pointers have performance overhead than raw pointers. Use them when needed, such as in complex data structures or when accessing resources across multiple threads.

Practical example:

Consider the following example, which shows how shared pointers prevent dangling pointers:

class Widget {
public:
    std::shared_ptr createChild() {
        return std::make_shared();
    }
};

int main() {
    std::shared_ptr parent = std::make_shared();
    std::shared_ptr child = parent->createChild();
    
    // ... 代码块 1，父对象 parent 被删除 ...
    
    // 代码块 2，child 仍然有效
    child->doSomething();
    
    return 0;
}

In this example, even if the parent objectparent is removed, child in block 2 is still valid because std::shared_ptr maintains shared ownership of the object.

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