Preserve decimal formatting

[nickgeorge]

Hello, I'm trying to use this as part of a specialized json parsing/printing library. It is essential that performing a round trip parse-print does not modify data. Therefore, internally, we store decimals as strings, guaranteeing that formatting is not destroyed. Is it possible to reproduce this in nlohmann/json? or is it inherently destructive?

Examples:

2.500 becomes 2.5
1E-22 becomes 1e-22
66.899999999999991 becomes 66.89999999999999

I understand the limitations of float representation - the hope is that it's possible to enable a mode/custom parsing that internally parses decimals into as strings, so as to side-step these limitations.

Most broadly, the question is if it's possible to get to a guarantee that (other than insignificant white-space)

json::parse(my_json_string).dumps() == my_json_string

Thanks,
Nick

[nlohmann]

This is not a bug, but intended behavior: the library uses double, std::int64_t, and std::uint64_t internally not store numbers. While we do expose the string from the parser in the SAX interface (see https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/input/json_sax.hpp#L64), we have no extension point for serializers yet. That means: you could write a SAX adapter to digest the parsed input and store strings alongside with numbers, you cannot use the basic_json class to store or serialize such data.