Resource Acquisition is Initialization

It is a technique in C++ language where resource use is bounded to the lifetime of the objects with automatic duration (non-dynamically allocated objects). This is implemented using class constructors and destructors where resources is acquired when constructor creates the object and resource is released in destructor.

For example:

class Items
{
    int *arr{};
public:
    Items()
    {
        std::cout << "Allocating resources\n";
        arr = new int[5];
    }
 
    ~Items()
    {
        std::cout << "Releasing resources\n";
        delete arr;
    }
};

References

1. https://www.learncpp.com/cpp-tutorial/destructors/
2. https://en.cppreference.com/cpp/language/raii