Re: [boost] Thousands Separators

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2001-09-21 15:14:37

On Friday, September 21, 2001, at 03:16  PM, Bill Seymour wrote:

> First, if I have a numpunct facet that specifies a grouping,
> is it correct to insert thousands separators to the right
> of the decimal point?  The text about do_grouping() in
> [lib.facet.numpunct.virtuals] isn't clear about that.

There is considerable debate in the lwg whether or not thousands 
separators should be applied to floating point types:

http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#282

If you follow the standard exactly, it appears to say that thousands 
separators can appear to the left of the decimal point on floating point 
parsing, but not at all in floating point formatting.  This exact 
reading strikes many as inconsistent enough to be a defect.  There are 
at least three different existing implementations:

1.  Dinkumware:  Does not allow thousands separators in parsing or 
formatting of floating point values.

2.  SGI:  Allows thousands separators in parsing, but not formatting of 
floating point values.

3.  Metrowerks:  Allows thousands separators in parsing, and formatting 
of floating point values.

In no case does there seem to be support for thousands separators to the 
right of the decimal point, only to the left (22.2.3.1/2):

> integer   ::= [sign] units
>   sign      ::= plusminus [whitespace]
>   plusminus ::= '+' | '-'
>   units     ::= digits [thousands-sep units]
>   digits    ::= digit [digits]
>
> and floating-point values have:
>
>
>
>   floatval ::= [sign] units [decimal-point [digits]] [e [sign] digits] |
> 	       [sign]        decimal-point  digits   [e [sign] digits]
>   e        ::= 'e' | 'E'

> Second, [lib.facet.numpunct.members] says that thousands_sep()
> returns a char_type; but [lib.facet.numpunct.virtuals] says
> that do_thousands_sep() returns a string_type.  Am I correct
> in thinking that that's a typo in [...virtuals] and that it's
> supposed to be a char_type?

You are correct, this is an official dr now:

http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#20

-Howard