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Smart Pointers

Smart pointers are objects that behave like raw pointers but automatically manage the lifetime of dynamically allocated memory.

<memory> library has three type of smart pointer: - std::unique_ptr - std::shared_ptr - std::weak_ptr

std::unique_ptr

Only one owner, memory is deleted automatically when pointer goes out of scope

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#include <iostream>
#include <memory>

class MyClass {
private:
  int value_;

public:
  MyClass(){
    std::cout << "CREATE MY CLASS." << std::endl;
  }

  MyClass(int value) : value_(value) {
    std::cout << "CREATE MY CLASS WITH VALUE: " << value_ << std::endl;
  }
  ~MyClass(){
    std::cout << "DESTROY MY CLASS." << std::endl;
  }


};

int main() {
  auto obj = std::make_unique<MyClass>(5);

  return 0;
}

std::shared_ptr

Multiple owners, Internally uses a reference counter memory is deleted when counter reaches 0.

std::weak_ptr

Non-owning observer of a shared_ptr, does't increase reference count

TODO: explain usage and more

RAII

Resource Acquisition Is Initialization

A resource is acquired in the constructor and released in the destructor

Resource

A resource is anything that must be release manually

Resource Acquire Release
heap memory new delete
file open() close()
mutex lock() unlock()
socket socket() close()
GPU memory allocate free

Demo:

```cpp title="without RAII (memory leak) void example() { int* p = new int(5);

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throw std::runtime_error("error");

delete p;

} cpp title="with RAII" void example() { std::unique_ptr p = std::make_unique(5); throw std::runtime_error("error"); } ```

Memory released when unique_ptr out of scope

Reference