Davi Arnaut <d...@twitter.com> writes: > On Thu, Jul 26, 2012 at 5:50 PM, Igor Babaev <i...@askmonty.org> wrote: >> + bzero(column_stats, sizeof(Column_statistics) * cnt); > > That's not allowed for non-POD types.
Can you elaborate on exactly when bzero() (or memset() or similar) is allowed or not allowed? I searched in my C++ reference, and did not really find anything ... in fact I did not find anything that said memset(p, 0, sizeof(*p)) would _ever_ be allowed for a class. It is my understanding that even for C, memset(..., 0, ...) is only valid for integer types. Initialising with memset() floating-point and even pointers values is not well-defined! Or did I miss something? I think this is an important issue, as memset() of a C++ class is certainly wrong in many cases, and can lead to subtle and platform-dependent failures. So let's point out clearly the rules that apply, or define such rules if necessary: 1. Does the C and C++ standards define suitable rules? If so, we should use them. However, I suspect that memset() is invalid in standard C and C++ except for arrays of integers, which is excessively restrictive. 2. If C/C++ standard is not sufficient, we need to agree on a coding style (and stay within what works on all reasonable compilers/platforms). I would much prefer to find an existing standards rule or convention. But failing that I would suggest: - Only memset() and memcpy() structs. - Virtual functions are definitely out (in struct as well as members). - Constructors and destructors also must not be defined for such structs (or its members). - Derived classes also should never be memset()'ed. Class inheritance is likely to need extra info on some (present or future) platforms and compilers. - Do not have private: methods in such memset() structs. I do not think it matters to the code generated, but private: is meaningless if arbitrary code is manipulating the memory of the struct directly. Usually I would have no methods at all in structs that I plan to do memset() on. But I suppose we also need to look at what existing code does. Comments? - Kristian. _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
