Re: A question about FLAGS in lstrlib.c

[Lorenzo Donati <lorenzodonatibz@...>]

On 15/10/2019 14:14, Marc Balmer wrote:
> Hi
>
> In lstrlib.c, the preprocessor define FLAGS defines the flag
> characters that be used in string formatting (string.format()). It
> includes flags like 0, -, space, etc.  The flag to add thousands
> separators to a number ('), however, is missing.  Is there a reason
> for that?
>
> I can use
>
> print(string.format("%.2f", 1000000))
>
> to print a number,  but with "stock" Lua I can not use
>
> print(string.format("%'.2f", 1000000))
>
> to print the number with thousands separator.
>
> Adding an apostrophe to FLAGS in lstrlib.c makes it perfectly word.
>
> I understand that the thousands separator flag is not part of C89,
> but a SuSv2 extension, which seems to be present on almost all
> (modern) operating systems.

I don't think it is part of ANY C standard, if I read correctly the info
at cppreference.com:

https://en.cppreference.com/w/c/io/fprintf

Although I consider that a very useful feature, messing with the default 
flags could be dangerous for code compatibility IMO, as long as
Lua delegates the underlying formatting to C libraries.

Should Lua ever implemented a more complete string formatting facility, 
I'd welcome that feature.

> Could FLAGS be something that could be overriden in luaconf.h?  It
> would be as simple as enclosing the definition of FLAGS in a #ifndef
> FLAGS / #endif bracket.
>
> Thanks, Marc

cheers!

-- Lorenzo