[Boost-users] [Spirit Qi] Failed to parse the following fixed format double

Subject: [Boost-users] [Spirit Qi] Failed to parse the following fixed format double
From: Michael Powell (mwpowellhtx_at_[hidden])
Date: 2019-01-19 22:05:58

Hello,

We've been here before, but it is still a problem. I formatted this
one using Boost.Format, "%1$.20f", especially dealing with 64-bit
floating point values:

"-6454866677007257221799838306103363329054216765979693126687924767750184064408021645577150612734391912932504859271476290909819606665305867922002041825515395649967939044362235953753132737391831714484437364695236622971838510661738713863719312223765488747173369566663518205119012003640541309414736378162701139968.00000000000000000000"

Grammar is defined:

numeric_sign %= (
    ('-' >> attr(numeric_sign_minus))
    | ('+' >> attr(numeric_sign_plus))
    )
    ;
float_lit %= real_parser<float_t, strict_ureal_policies<float_t>>{};
floating_point %= -numeric_sign >> float_lit;

With rules defined as:

qi::rule<iterator_type, numeric_sign_t()> numeric_sign;
qi::rule<iterator_type, float_t()> float_lit;
qi::rule<iterator_type, floating_point_number_t()> floating_point;

Where float_t is a defined part of the AST:

using float_t = double;

And floating_point maps to the floating_point_number_t, basically
mapping the Sign and Value.

Seems like we've been here before with inadequate response, however,
reading the Boost documentation, I do not see any reason any Qi should
be rejecting this value:

https://www.boost.org/doc/libs/1_69_0/libs/spirit/doc/html/spirit/qi/reference/numeric/real.html

Particularly the RealPolicies:

sign
    =   lit('+') | '-'
    ;

nan
    =   -lit("1.0#") >> no_case["nan"]
        >> -('(' >> *(char_ - ')') >> ')')
    ;

inf
    =   no_case[lit("inf") >> -lit("inity")]
    ;

floating_literal
    =   -sign >>
        (       nan
            |   inf
            |   fractional_constant >> -exponent_part
            |  +digit >> exponent_part
        )
    ;

fractional_constant
    =  *digit >> '.' >> +digit
    |  +digit >> -lit('.')
    ;

exponent_part
    =   (lit('e') | 'E') >> -sign >> +digit
    ;

Although the concern I have is that the RealPolicy grammar defined
above is not implemented as Qi Rules, per se, but rather brute force.
In other words, error prone in the ways that a brute force approach is
error prone.

Best regards,

Michael Powell