Mikhail Ramendik <[EMAIL PROTECTED]> said: > Aaron Stone wrote: > >> Based on your Python comments earlier, I'm assuming that you already >> program quite a bit, but haven't used C much. My guess is that the only >> confusing things are *, ** and &. For those, there's a really good cartoon >> guide that explains them very visually, but I can't remember the name of >> it :-[ > > The current question is not about those, but about optional arguments. > > I.e. I want to be able to define a function named foo(), so that it > could be called both as foo(a,b) and as foo(a,b,c). > > I'm afraid this was added later than the K&R text was written. > > I'm nearly sure the feature is there; in fact somebody told me that one > could even rewrite printf() in C, and that has a theoretically infinite > number of optional arguments. > > The projected dbmail use is for adding features to db layer functions, > while preservicg backwards compatibility.
Very bad idea. C does support variadic arguments, but there is absolutely no type checking whatsoever. Printf() typechecking is a feature of the compiler, and only if the compiler knows the same printf() that your libc provides. In fact, for a long time our trace() function was not typechecked until I found the GCC extension that tells the compiler to treat a function like printf(). C++ has full support for optional arguments and default values, which it calls function overloading. Not too much good for us, we're in plain C ;-) If you need a slightly varied function, the two main options are to either modify the function and all places that use it (for nearly-trivial changes that can be specifically unit tested, this is OK) or to create a wrapper function by the old name that provides the old functionality while calling the new version of the function with a new name. This is kinda-sorta how the db_getresult_int, ull, etc. functions are implemented. Aaron --
