Is it safe to use "yes","no","i","out" as name for variables/enum?

Question

I have read the document about naming rule of C++, they seems to be usable names.

However, in practice, when I tried to create a variable/enum with a name like iter, yes, no, out, i, Error, etc. , Visual Studio will strangely use italic font for them.

I can only guess that they are reserved for special thing, and IDE (e.g. refactoring/rename process) might act strangely if I use such names.

Is it safe to use those names in practice? Am I just too panic?

Sorry if it is too newbie or an inappropriate question.
I doubt about it for a few weeks but too afraid to ask.

Answer 1

These names are valid and will not cause any "harm", the standard only says:

• Each name that contains a double underscore (_ _) or begins with an underscore followed by an uppercase letter (2.11) is reserved to the implementation for any use.

• Each name that begins with an underscore is reserved to the implementation for use as a name in the global namespace.

Which means that all your names are fine to use in user-code. Visual Studio might just have a thing for these names as i and iter are usually used in looping.

Answer 2

These names are not reserved in standard C++, as explained by Rick Astley. An implementation may choose to accept additional reserved words to provide language extensions, such as ref class in C++/CLI. In some cases, such as with ref class, where ref is a contextual keyword, these extensions only make otherwise ill-formed programs well-formed in the scope of the extended language. In other cases, an otherwise well-formed program may change its meaning or become ill-formed. In the former case, the implementation is still conforming to the C++ standard, as long as it issues all mandatory diagnostics; in the latter case, it is certainly not conforming.

It is considered good practice to make the latter kind of extensions optional e.g. using a command line option, so that the implementation still has a mode in which it is fully standards compliant. My immediate guess is that VC++ in fact does allow you to write well-formed programs containing yes, no, i, iter which will behave as required by the standard (implementation bugs notwithstanding).

The IDE is a different beast, though. It is considered to be outside of the scope of the C++ standard, and might discourage or even stop you from writing perfectly well-formed code. That would still be a quality of implementation issue, or an issue of customer satisfaction, if you will.