Destructors and Automatic Cleanup

A destructor (~ClassName) runs automatically when an object dies — scope exit for automatic objects, delete for heap objects, container shrinking for elements. It is the "~" half of RAII: acquire in the constructor, release in the destructor.

#include <cstdio>

class FileLog {
public:
    explicit FileLog(const char* path) : handle_{std::fopen(path, "a")} {}
    ~FileLog() { if (handle_) std::fclose(handle_); }   // ALWAYS runs

    FileLog(const FileLog&) = delete;            // (Module 4: copy control)
    FileLog& operator=(const FileLog&) = delete;

private:
    std::FILE* handle_;
};

void use() {
    FileLog log{"app.log"};   // acquire
    // ... write via log ...
}                             // destructor closes the file — even on throw

What belongs in a destructor

Only releasing what the object owns: file handles, locks, sockets, heap memory. Members that own themselves (a std::string member, a std::vector member) destroy themselves — you never write delete member_ for a value member.

The two rules for now

1. If the class holds a raw resource it acquired, it needs a destructor.
2. If it does not hold one, write no destructor at all — the implicit one is correct, and a hand-written empty one only invites mistakes.

Deletion order: members destroy in reverse declaration order, then the body runs... actually the body runs first, then members destroy in reverse order. Base parts (Module 3) destroy after the derived body.