Rework number parsing about minijson_reader HOT 8 CLOSED

Imho, number parsing is better to be redesigned.

1. Reader should accept all JSON numbers, by simple "regex" described here http://www.json.org. E.g. 1000-digit number is ok.
2. template value.as_number<TNumber> should call static minijson::stonum<TNumber>
3. stonum<TNumber> should be implemented for all C++ integer/floating point types, by relevant parsing and maybe throwing (e.g. "out of range"). I don't think parsed values caching is required - every value usually converted only once.
4. User always can add his specialization for stonum, e.g. stonum<MyBigNumber>

P.S. Thanks for this great project!

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Apologies for this oversight. This is really sad and embarrassing.

strtod and alike really belong to a different era, where it was appropriate to change the behaviour of an entire class of functions by messing with some global mutable state. The errno dance for dealing with error conditions is pretty awful as well.

Let me ponder over a possible solution.

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Thanks, I'll rework that as well. Feel free to share some code if you think it's worth sharing.

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For original problem, locale decimal point seems to be available as
std::use_facet<std::numpunct<char>>(std::locale()).decimal_point().

If it differ from '.', strtod should be applied on value's buffer copy, with '.' replaced by right char.

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There seems to be a light at the end of the tunnel.

The really good news is that starting with C++17, the C++ programming language gained std::from_chars, an actually usable function to parse numbers without having to deal with the oddities and the idiosyncrasies of the old C standard library, including the terrible locale-dependent behavior trap.

The good and bad news is that GCC added full support for that function with version 11, which was released in 2021. It's good because we can finally parse floating point numbers properly without having to use streams (ew!) or some external library, it's bad because people with older versions of GCC are out of luck.

Since the current version of minijson_reader is dangerously buggy when it comes to parsing doubles, and I do not want to keep on using strtod with a weird (and probably buggy) adapter performing a locale dance, nor do I want to pull in some dependency, I think I'll bite the bullet and use std::from_chars. Those who cannot upgrade their compiler will have to stay on an old tag (and make sure they don't change their locale, sadly) or use a better json library (lol).

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OK @inikulshin @dlebansais @michaelkourlas, my idea for the new minijson::value class is fully implemented in the rework_number_parsing branch (which became a massive refactor from ancient C++03 to modern C++). The best place to start is the README (which on that branch is up-to-date with the changes).

Thanks to C++17 and especially its new number-parsing functions, minijson::value finally looks vaguely usable to me. 😅 Let me know what you think.

User always can add his specialization for stonum, e.g. stonum

Let's add this on a second pass.

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User always can add his specialization for stonum, e.g. stonum

Let's add this on a second pass.

Filed as #24

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