Argo

A flexible and easy to use JSON library that makes the mapping of a structures from a dynamically typed language onto C++ objects as painless as possible. Support for JSON pointer (aka JSON Path) is included.

If you're familiar with the Python json module this library should be very easy to pick up. E.g. loading and saving a JSON message is as simple as:

auto j = parser::load("file.json");
unparser::save(*j, "newfile.json");

Documentation

There is full documentation here.