When to use shared_ptr and when to use raw pointers?

In C++, choosing between shared_ptr and raw pointers depends on specific use cases and resource management requirements. Below, I will elaborate on their applicable scenarios and respective pros and cons.

When to Use shared_ptr

shared_ptr is a smart pointer that provides automatic reference-counted memory management. It is particularly useful when multiple objects share ownership of the same resource. Below are scenarios where shared_ptr is appropriate:

1. Shared Ownership: When multiple objects need to share ownership of the same resource, shared_ptr ensures the resource is automatically released when the last shared_ptr is destroyed. For example, in a graphical user interface application, multiple views may access the same data model.

cpp
std::shared_ptr<DataModel> model = std::make_shared<DataModel>();
View view1(model);
View view2(model);

1. Circular Reference Issues: In complex object relationships, such as doubly linked lists or graph structures, using shared_ptr alongside weak_ptr can prevent memory leaks due to circular references.

cpp
class Node {
public:
    std::shared_ptr<Node> next;
    std::weak_ptr<Node> prev;  // Using weak_ptr to avoid circular references

    // Constructors, destructors, etc.
};

1. Exception Safety: In exception handling, shared_ptr ensures resource safety by automatically releasing resources even if exceptions occur.

cpp
void process() {
    std::shared_ptr<Resources> res = std::make_shared<Resources>();
    // Perform operations that may throw exceptions
}  // Even if an exception occurs, res is properly released

When to Use Raw Pointers

Although shared_ptr provides many conveniences, raw pointers are more appropriate in certain scenarios:

1. Performance-Critical Sections: Raw pointers incur no additional overhead (e.g., reference counting), making them preferable in performance-critical code regions.

2. Existing Resource Management Strategies: If the resource's lifetime is managed by specific strategies (e.g., a dedicated memory pool), using raw pointers may be more intuitive and flexible.

3. Interacting with C Code: When interacting with C libraries, raw pointers are typically required, as C does not support smart pointers.

4. Simple Local Usage: For pointers used within a narrow scope without needing to span multiple scopes or return to the caller, raw pointers keep the code concise.

cpp
void example() {
    Resource res;
    Resource* res_ptr = &res;
    // Perform operations using res_ptr
}  // res is automatically destroyed at scope end, no memory leak concerns

In summary, choosing between shared_ptr and raw pointers should be based on specific requirements, performance considerations, and the complexity of resource management. Smart pointers like shared_ptr provide convenience and safety but may introduce overhead that makes them unsuitable in some cases. In C++, both shared_ptr and raw pointers are tools for resource management, particularly for managing dynamically allocated memory. Different choices suit different scenarios; below are some guiding principles for selecting between shared_ptr and raw pointers:

When to Use shared_ptr

1. Shared Ownership: When multiple parts need to share ownership of an object, shared_ptr is a suitable choice. shared_ptr ensures that multiple owners can share the same resource without worrying about premature release through reference counting. For example, if you have a class whose instance needs to be shared across several data structures, using shared_ptr safely manages the instance's lifetime.

Example:

cpp
std::shared_ptr<MyClass> ptr1 = std::make_shared<MyClass>();
std::shared_ptr<MyClass> ptr2 = ptr1;  // ptr2 now shares ownership with ptr1

1. Handling Circular References: Using smart pointers like shared_ptr alongside weak_ptr can resolve circular reference issues. When objects mutually hold each other's shared_ptr, reference counting never reaches zero, causing memory leaks. By changing one connection to weak_ptr, the cycle is broken.

Example:

cpp
class A;
class B;

class A {
public:
    std::shared_ptr<B> b_ptr;
};

class B {
public:
    std::weak_ptr<A> a_ptr;  // Using weak_ptr to prevent circular references
};

When to Use Raw Pointers

1. Performance-Critical Sections: In performance-critical code regions, raw pointers incur less overhead than shared_ptr because shared_ptr requires additional reference counting. If resource lifetime can be explicitly managed (e.g., via scope control), using raw pointers reduces overhead.

Example:

cpp
void processLargeAmountOfData() {
    MyClass* ptr = new MyClass();
    // Process large data
    delete ptr;
}

1. Interacting with C Code: When interacting with C code, especially when calling C libraries, raw pointers are typically required, as C does not support smart pointers.

Example:

cpp
extern "C" {
    void c_function(int* data);
}

void exampleFunction() {
    int x = 10;
    c_function(&x);  // Using raw pointer to interact with C function
}

1. Simple Resource Management Scenarios: For straightforward resource management, such as creating and destroying within a function without crossing scopes or returning ownership, raw pointers are concise and direct.

In summary, choosing between shared_ptr and raw pointers should be based on specific requirements and context. Smart pointers like shared_ptr provide automated memory management, significantly reducing the risk of memory leaks, but introduce some performance overhead. Raw pointers are suitable for performance-sensitive or straightforward resource management scenarios.