std::unique_ptr

🔹std::unique_ptr — Exclusive Ownership Smart Pointer

🧠 Concept

A std::unique_ptr owns a dynamically allocated object exclusively. No other smart pointer can own the same resource. When the unique_ptr goes out of scope, the object is automatically deleted — making it safe and exception-proof.

It cannot be copied, only moved.

✅ Basic Syntax

#include <iostream>
#include <memory>

class Resource {
public:
    Resource() { std::cout << "Resource acquired.\\n"; }
    ~Resource() { std::cout << "Resource released.\\n"; }
    void greet() const { std::cout << "Hello from Resource\\n"; }
};

int main() {
    std::unique_ptr<Resource> uptr = std::make_unique<Resource>();  // preferred way
    uptr->greet();

    // std::unique_ptr<Resource> uptr2 = uptr;  ❌ Error: cannot copy
    std::unique_ptr<Resource> uptr2 = std::move(uptr);  // ✅ Move allowed

    if (!uptr) std::cout << "uptr is now null\\n";

    return 0;
}

🧷 Key Characteristics

Feature	Value
Ownership	Exclusive
Copyable	❌ No
Movable	✅ Yes
Overhead	Very low (just a pointer)
Thread-safe	❌ No (ownership is not shared)
Default deleter	delete (can be customized)
Use case	Enforcing unique ownership semantics

🔁 Custom Deleter Example

auto fileDeleter = [](FILE* f) {
    if (f) {
        std::cout << "Closing file...\\n";
        fclose(f);
    }
};

std::unique_ptr<FILE, decltype(fileDeleter)> fptr(fopen("test.txt", "w"), fileDeleter);

You can wrap resources like files or sockets with custom deleters to ensure they are closed correctly.

🛠️ Useful Member Functions