{"title":"unique_ptr","description":null,"content":"When we talk about smart pointers, `unique_ptr` often takes center stage due to its simplicity and efficiency. \n\nLet’s dive into its core features, use cases, and practical applications.\n\n---\n\n# What is unique_ptr?\n\nAt its heart, a `unique_ptr` is a smart pointer that represents sole ownership of an object. When you use `unique_ptr`, you ensure that there is exactly one pointer managing a resource. \n\nThis means that the resource will be automatically freed when the `unique_ptr` goes out of scope, reducing the chances of memory leaks.\n\n## Creating unique_ptr\n\nCreating a `unique_ptr` is straightforward, and the preferred method is using `std::make_unique`. This function not only simplifies the syntax but also minimizes the risk of memory leaks that can occur with raw pointers. Here’s how you can create a `unique_ptr`:\n\n\n```cpp\n#include \n#include \n\nclass Resource {\npublic:\n Resource() { std::cout << \"Resource acquired\\n\"; }\n ~Resource() { std::cout << \"Resource released\\n\"; }\n};\n\nint main() {\n // Create a unique_ptr using make_unique\n auto resourcePtr = std::make_unique();\n // Use resourcePtr as needed\n return 0;\n}\n```\n\n\n\n> **TIP**\n>\n> Always prefer `std::make_unique` over direct `new` statements when creating `unique_ptr`. It’s safer and cleaner.\n\n\nThe `unique_ptr` takes ownership of the resource, and it will automatically clean up when it goes out of scope.\n\n---\n\n# Ownership Transfer\n\nOne of the most powerful features of `unique_ptr` is its ability to transfer ownership. You can’t copy a `unique_ptr` because ownership should not be duplicated, but you can move it. This is done using `std::move`, which transfers ownership from one `unique_ptr` to another.\n\nHere’s an example to illustrate this:\n\n\n```cpp\n#include \n#include \n\nclass Sample {\npublic:\n Sample() { std::cout << \"Sample created\\n\"; }\n ~Sample() { std::cout << \"Sample destroyed\\n\"; }\n};\n\nvoid process(std::unique_ptr samplePtr) {\n // Use the samplePtr\n std::cout << \"Processing sample\\n\";\n}\n\nint main() {\n auto ptr1 = std::make_unique();\n process(std::move(ptr1)); // Ownership transferred\n\n if (!ptr1) {\n std::cout << \"ptr1 is now null\\n\"; // ptr1 is null after moving\n }\n\n return 0;\n}\n```\n\n\nIn this case, `ptr1` transfers ownership of the `Sample` object to the `process` function. After the move, `ptr1` becomes null, preventing potential double deletion.\n\n---\n\n# Custom Deleters\n\nSometimes, you might need more control over how a resource is released. This is where custom deleters come into play. A `unique_ptr` allows you to specify a custom deleter, which can be especially useful for managing resources that require specific cleanup procedures.\n\nHere’s how you can use a custom deleter:\n\n\n```cpp\n#include \n#include \n\nstruct CustomDeleter {\n void operator()(int* ptr) const {\n std::cout << \"Custom deleting int\\n\";\n delete ptr; // Custom cleanup\n }\n};\n\nint main() {\n std::unique_ptr ptr(new int(42), CustomDeleter());\n std::cout << \"Value: \" << *ptr << \"\\n\"; // Use the resource\n return 0; // CustomDeleter will be called here\n}\n```\n\n\nIn this example, `CustomDeleter` defines how to delete an `int`. The `unique_ptr` uses this deleter instead of the default `delete`, allowing for more flexible resource management.\n\n\n> **WARNING**\n>\n> Be careful with custom deleters, especially if they reference other resources or if they require additional cleanup steps that could lead to undefined behavior.\n\n\n---\n\n# Common Pitfalls\n\nDespite its benefits, `unique_ptr` is not without its challenges. Here are some common pitfalls to be aware of:\n\n1. **Moving vs. Copying**: Remember that `unique_ptr` cannot be copied. Attempting to copy will result in a compilation error. Always use `std::move` when transferring ownership.\n2. **Avoiding Dangling Pointers**: When you transfer ownership, ensure that the original pointer is no longer used. Accessing it after the move can lead to undefined behavior.\n3. **Resource Management**: Be mindful of the resources being managed. If you use a `unique_ptr` with a non-heap allocated resource (like a stack variable), it can lead to problems.\n4. **Interoperability**: If you're integrating with APIs that expect raw pointers, be cautious when passing `unique_ptr`. Use `get()` to retrieve the raw pointer, but remember that this temporarily relinquishes ownership.\n\n\n```cpp\nvoid rawPointerFunction(int* ptr); // Some external API function\n\nint main() {\n std::unique_ptr uptr = std::make_unique(10);\n rawPointerFunction(uptr.get()); // Pass the raw pointer\n\n // Uptr still owns the memory; don't delete manually.\n return 0;\n}\n```\n\n\n\n> **TIP**\n>\n> If you need to pass a `unique_ptr` to a function, consider passing it by reference to avoid transferring ownership unless that's your intention.\n\n\n---\n\n# Real-World Applications\n\n`unique_ptr` is widely used in scenarios where resource management is critical. Here are a few common use cases:\n\n- **Resource Management in Classes**: Use `unique_ptr` to manage dynamically allocated members within a class, ensuring proper cleanup when the object is destroyed.\n\n\n```cpp\nclass Widget {\nprivate:\n std::unique_ptr resource;\n\npublic:\n Widget() : resource(std::make_unique()) {}\n // No need for manual cleanup\n};\n```\n\n\n- **Factory Functions**: When creating objects in factory methods, returning `unique_ptr` allows for safe ownership transfer while preventing memory leaks.\n\n\n```cpp\nstd::unique_ptr createWidget() {\n return std::make_unique();\n}\n```\n\n\n- **Data Structures**: When implementing data structures like trees or graphs, `unique_ptr` can be used to manage child nodes, ensuring that the entire structure is cleaned up.\n\n\n```cpp\nclass Node {\npublic:\n std::unique_ptr left;\n std::unique_ptr right;\n\n Node() : left(nullptr), right(nullptr) {}\n};\n```\n\n\n---\n\n# What's Next\n\nNow that you have a solid grasp of `unique_ptr` and how it handles unique ownership of resources, you're ready to explore `shared_ptr`. \n\nIn the next chapter, we will discuss how `shared_ptr` allows multiple pointers to share ownership of the same resource, delving into its use cases and intricacies.","pageType":"cpp"}

unique_ptr

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