Support conversion from JSON to TOML?

[ghost]

Is your feature request related to a problem? Please describe.
I could get the JSON string from TOML table by json_formatter, but how can I read it again from JSON file and parse to TOML table. Please help me if i did not notice that on the document, thanks.

Describe the solution you'd like
JSON string or file should be supported by parse function?

Additional context

[marzer]

There's no built-in way to do this. The json_formatter exists for two reasons:

1. Despite being an arguably poor config format, JSON makes for a pretty good over-the-wire/storage serialization format (and indeed is used very commonly for those purposes), so going from TOML to JSON is a reasonable use-case
2. toml++ already has the TOML parser and data-types so implementing the json_formatter was super easy, barely an inconvenience

For me to go in the other direction (i.e. from JSON to TOML) I'd need to implement a complete JSON parser (plus all the weird offshoots and dialects), which isn't something I'm willing to maintain. Fortunately I don't need to, though; C++ is spoiled for choice when it comes to JSON libs:

• https://github.com/nlohmann/json
• https://github.com/Tencent/rapidjson/
• https://github.com/open-source-parsers/jsoncpp
• probably quite a few more floating around

If you need this functionality you could pair toml++ with your JSON lib of choice and implement it yourself relatively easily.