Constructors and Destructors

A constructor establishes a valid object. A destructor releases its resources. Members are initialized before the constructor body in declaration order—not initializer-list order—so declare dependent members carefully.

#include <string>
#include <utility>

class Session {
    std::string user_;
    bool active_{false};
public:
    explicit Session(std::string user)
        : user_{std::move(user)}, active_{true} {}

    ~Session() { active_ = false; }

    Session(const Session&) = delete;
    Session& operator=(const Session&) = delete;
};

explicit prevents surprising implicit conversion from a single argument. Delegating constructors reuse another constructor. = default requests the compiler-generated operation; = delete rejects an operation with a clear diagnostic.

The special members

C++ can generate a default constructor, destructor, copy constructor, copy assignment, move constructor, and move assignment. If a class directly manages a resource, it may need the Rule of Five. Prefer the Rule of Zero: store resources in std::string, containers, and smart pointers so their correct operations compose automatically.

Destruction runs in reverse construction order. Derived parts are destroyed before base parts; members are destroyed in reverse declaration order. Constructors should not publish a partially formed object, and destructors should not throw. A failed constructor destroys already-constructed subobjects, making RAII essential for exception safety.