RAII: The Ownership Idiom

RAII — Resource Acquisition Is Initialization — is the single most important C++ idiom: wrap every resource in an object whose destructor releases it. Scope exit, including via exception, runs the destructor. Nothing leaks.

class FileGuard {
public:
    explicit FileGuard(std::FILE* f) : f_{f} {}
    ~FileGuard() { if (f_) std::fclose(f_); }

    FileGuard(const FileGuard&) = delete;             // one owner
    FileGuard& operator=(const FileGuard&) = delete;
private:
    std::FILE* f_;
};

void work() {
    FileGuard g{std::fopen("data.txt", "r")};  // acquired
    // ... even an exception here cannot leak the handle
}                                              // destructor runs here

You have used RAII all along without naming it: std::vector owns its heap buffer; std::string owns its chars; std::ofstream owns a file handle. Smart pointers are just RAII for the case where you call new: they own a heap object and delete it in their own destructor.

Ownership is the design word behind the acronym: exactly one piece of code is responsible for releasing each resource. Everything else borrows.