JSON schema validation

Is there a stable library that can validate JSON against a schema?

I found a couple hits on google:

• From the Chromium project: http://aaronboodman-com-v1.blogspot.com/2010/11/c-version-of-json-schema.html
• http://avro.apache.org/docs/1.4.1/api/cpp/html/index.html

You could also plug a Python or Javascript interpreter into your app, and simply run the native version of those validator implementations that you've already found.

Is there a reason I can't easily find a C++ JSON schema validator?

I believe JSON originated as a web technology, and C/C++ has fallen out of favor for web app implementation.

Valijson is a very good library which depends only on Boost (And I'm actually hoping to change that). It doesn't even depend on any particular JSON parser, providing adapters for most commonly-used libraries like JsonCpp, rapidjson and json11.

The code may seem verbose, but you can always write a helper (example for JsonCpp):

#include <json-cpp/json.h>#include <sstream>#include <valijson/adapters/jsoncpp_adapter.hpp>#include <valijson/schema.hpp>#include <valijson/schema_parser.hpp>#include <valijson/validation_results.hpp>#include <valijson/validator.hpp>void validate_json(Json::Value const& root, std::string const& schema_str){  using valijson::Schema;  using valijson::SchemaParser;  using valijson::Validator;  using valijson::ValidationResults;  using valijson::adapters::JsonCppAdapter;  Json::Value schema_js;  {    Json::Reader reader;    std::stringstream schema_stream(schema_str);    if (!reader.parse(schema_stream, schema_js, false))      throw std::runtime_error("Unable to parse the embedded schema: "                               + reader.getFormatedErrorMessages());  }  JsonCppAdapter doc(root);  JsonCppAdapter schema_doc(schema_js);  SchemaParser parser(SchemaParser::kDraft4);  Schema schema;  parser.populateSchema(schema_doc, schema);  Validator validator(schema);  validator.setStrict(false);  ValidationResults results;  if (!validator.validate(doc, &results))  {    std::stringstream err_oss;    err_oss << "Validation failed." << std::endl;    ValidationResults::Error error;    int error_num = 1;    while (results.popError(error))    {      std::string context;      std::vector<std::string>::iterator itr = error.context.begin();      for (; itr != error.context.end(); itr++)        context += *itr;      err_oss << "Error #" << error_num << std::endl              << "  context: " << context << std::endl              << "  desc:    " << error.description << std::endl;      ++error_num;    }    throw std::runtime_error(err_oss.str());  }}

You can try UniversalContainer (libuc). http://www.greatpanic.com/code.html. You're looking for the container contract/schema checking class in this library. The schema format is clunky, but should handle everything you care about and provide reasonable reporting on why a particular instance fails to meet the schema.