What support is there for json schema in Qt / C++ / C

Question

Qt support for XML is very strong, up to and including support for XML schema validation.

Qt Support for JSON appears to be less extensive. Nothing I can find seems to confirm or deny support for json-schema or any other kind of Json schema validation in Qt.

Is there a sound way to validate json in Qt / C++?

Edit: to be clear, this question is centered on Json schema validation, not just confirming if an arbitrary document is valid Json.

Answer 1

Qt 5.8 still don't seem to have JSON Schema validation... But you can find a bunch of other interesting libraries.

4 C/C++ libraries are listed on JSON Schema website:

• wjelement mentionned by @Boris is optimized for performance and is used in email production environment by Messaging Architects. It is a C library but a C++ wrapper is also available (wjelement-cpp).
• valijson is a header-only Schema Validator that may be use with other JSON parser.
• json-schema-validator is based on nlohmann's modern c++ JSON parser which have nice features as a good interaction with STL containers. But this validator seems less mature.

Other JSON Schema Validator projects can be found on github or bitbucket, among them:

• jv_json devoted to embedded applications.
• libvariant that can also handle YAML and PLIST formats.

Answer 2

Indeed, it seems there are no Qt support for JSON Schema validation, even in Qt 5.1. Since writing your own would be very time-consuming, I would suggest:

• If you as developer would have provided the Schema, then do not validate by using a JSON Schema validation, but instead perform a hard-coded validation of your parsed JSON (i.e., manually check that the required fields are present, are of the correct type, and are within the specified bounds)

• If handling external JSON Schema is necessary (i.e., the Schema is not known in advance, possibly user-defined), then do not use Qt but an independent C/C++ JSON validator, like WJElement (the one linked on the json-schema website)