Ownership, RAII and the Rule of Five
Every C++ interview at a trading firm eventually arrives at ownership, usually through a small class that holds a resource. The question behind all of them is the same: for this object, who frees the thing it holds, and at exactly which point in the program?
RAII in one sentence
Tie the lifetime of a resource to the lifetime of an object, so that acquiring it is construction and releasing it is destruction. The acronym is unhelpful and the idea is not: because destructors run deterministically when scope ends, including when an exception unwinds the stack, a resource held this way cannot be leaked by any control path that leaves the scope.
class FileHandle {
public:
explicit FileHandle(const char* path) : fd_(::open(path, O_RDONLY)) {
if (fd_ < 0) throw std::runtime_error("open failed");
}
~FileHandle() { if (fd_ >= 0) ::close(fd_); }
private:
int fd_;
};
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