C++ library for parsing and stringifying JSON5 data

This is a port of the JavaScript reference implementation to C++.

The core functionality is completely implemented and the test coverage is as close to 100% as possible without causing compiler warnings. See the tests for usage examples.

• Sticking to the reference implementation as much as sensible.
• No dependencies apart from the STL.
• Minimalism.

• Due to a lack of experience in writing safety-critical software, this library should probably not be used where security is important. Please open issues for any vulnerabilities you spot.
• So far, the number data type only supports doubles, no ints. You can of course store ints in doubles but only from -2^53 to 2^53 without losing precision.
• Only UTF-8 is supported (which includes ASCII), no UTF-16, no UTF-32, no ISO 8859 or Windows character encodings.
• Unquoted keys can be ECMAScript Identifier Names with Unicode 10.0 characters (because that is the version used in the reference implementation).
• Parsing objects with unquoted non-ASCII keys may take significantly longer as a linear search is performed for verifying the Unicode category of each character. Consider quoting the keys or sticking to ASCII.
• Stringifying objects with non-ASCII keys may also take longer with no way around it yet. Consider using ASCII keys.
• In JavaScript, you can pass a reviver function to transform JSON into your own datastructure during parse. This does not really work in C++ so it was left out. Transformation into your datastructure has to be done afterwards.
• There is also no replacer function for filtering and transforming your JSON data during stringification. That must be done beforehand.

• Provide fromJson and toJson facilities for basic STL types.
• Put a how-to-use demo into the readme.
• Implement integer data types (how to decide if a parsed integer is int64_t or uint64_t?).
• Implement a more efficient way of verifying identifier name Unicode categories (or provide an option to skip that entirely).
• Make the peek() function caching for speed up.
• Implement a replacer function for stringification if somebody needs that.
• Implement UTF-16 and UTF-32 encoding and decoding if somebody needs that.

MIT

I hope you enjoy almost the elegance of JSON combined with the utility of comments, NaN and Infinity (among other actually really useful tweaks), all delivered with the performance of C++! Feel free to report issues and request pull requests!