January 25, 2016
## Background In my previous blog post, entitled [*You deserve great error messages*](2016_01_25_error_messages.html) I wrote about how all API:s should provide great error messages, and that config libraries (JSON parsers etc) have been in particular lacking in this area. I also introduced the idea of warning about keys that are never read in code, as that is most likely a bug. In this blog post I introduce a C++ library for parsing, editing and writing config files which follow the ideas set out in [the previous blog post](2016_01_25_error_messages.html). I strongly recommend you read through that article before reading on. ## Configuru For a home game project I started on last year I developed [*Configuru*](https://github.com/emilk/configuru), a C++ Config library which handles JSON as well as a simplified/extended dialect of JSON that I simply call *CFG*. The library has great JSON compliance and although it does not compete with other libraries in speed, it does, I believe, have the best error messages of any library out there. Here are just a few examples ([more on GitHub](https://github.com/emilk/configuru#error-messages)): ~~~ C config.json:1:16: Expected : after object key { "is_this_ok" = false } ^ `config.json:4: Failed to find key 'keyname'` (The line number is that of the object missing they key.) `config.json:2: Key 'colour' never accessed` ~~~ This last one is particular interesting because it is an example of something you are used to seeing from compilers (warning about unused variables), but I doubt you have ever seen from a JSON parser before. The motivation for this particular warning is described in detail in [the previous blog post](2016_01_25_error_messages.html). Configuru also has some other very nice (and optional) features: ### Enforces indentation A lot of non-programmers struggles with keeping their `[]` and `{}` matched because they do not have the habit of indenting. This leads to messy looking config files and when a brace is forgotten it can be hell to figure out where they should go. Configuru enforces indentation which means that if you forget a bracket or brace, Configuru will name the exact line where it should have appeared (or the exact line where you used the wrong indentation). The error messages are also helpful (`config.json:42: Bad indentation: expected 3 tabs, got 2`). Enforcing indentation may make you think of Python, but interestingly this has also [been added to GCC6](https://gnu.wildebeest.org/blog/mjw/2016/01/09/looking-forward-to-gcc6-nice-new-warnings/) as an optional warning (a warning which would have caught [one of the worst OSX security vulnerabilities](https://www.imperialviolet.org/2014/02/22/applebug.html)). ### Preserves comments When you load a config file and edit it (in C++) and save it again, all comments will still be there in the written file attached to the right key/value. This is great for when you have a hand-written config-file (with helpful comments) and have an in-game editor (slider etc) for adjusting values in the config file. ### Much much more If you use the CFG format you get: * Python-style multi-line strings. * C#-style verbatim strings. * Binary and hexadecimal numbers. * +inf, -inf, +NaN are valid numbers. * Optional trailing commas in lists and objects. * All commas optional. * Extremely pretty printing. Configuru is a single header and in public domain. Read more at