Add some example code that was prepared for a Melbourne C++ lightning talk

examples/json_pointers.cpp

@@ -0,0 +1,110 @@
+/**
+ * @file
+ *
+ * @brief Demonstrates how to resolve JSON pointers against the current document
+ *
+ */
+
+#include <iostream>
+
+#include <rapidjson/document.h>
+
+#include <valijson/adapters/rapidjson_adapter.hpp>
+#include <valijson/internal/json_pointer.hpp>
+#include <valijson/internal/json_reference.hpp>
+#include <valijson/utils/rapidjson_utils.hpp>
+
+using std::cerr;
+using std::cout;
+using std::endl;
+
+template<typename AdapterType>
+std::string maybeResolveRef(const AdapterType &value, const AdapterType &root)
+{
+    if (!value.isObject()) {
+        // Not an object, therefore not a JSON reference
+        return "";
+    }
+
+    const auto &object = value.getObject();
+    const auto itr = object.find("$ref");
+    if (itr == object.end()) {
+        // Object does not contain $ref property
+        return "";
+    }
+
+    const AdapterType maybeRef = itr->second;
+    if (!maybeRef.isString()) {
+        return "[$ref did not contain a string value]";
+    }
+
+    // Attempt to extract a JSON pointer
+    const std::string ref = maybeRef.getString();
+    const auto maybePointer = valijson::internal::json_reference::getJsonReferencePointer(ref);
+    if (!maybePointer) {
+        return "[$ref did not contain valid JSON pointer]";
+    }
+
+    const auto refAdapter = valijson::internal::json_pointer::resolveJsonPointer(root, *maybePointer);
+    if (!refAdapter.maybeString()) {
+        return "[$ref did not point to a string value]";
+    }
+
+    return refAdapter.asString();
+}
+
+template<typename AdapterType>
+void iterateJsonObject(const AdapterType &adapter)
+{
+    if (!adapter.maybeObject()) {
+        cout << "Not an object." << endl;
+        return;
+    }
+
+    cout << "Object members:" << endl;
+
+    // JSON objects are an unordered collection of key-value pairs,
+    // so the members of the object may be printed in an order that is
+    // different to that in the source JSON document.
+    for (auto member : adapter.asObject()) {
+        // The key is a std::string that can be accessed using 'first'
+        cout << "  " << member.first << ": ";
+
+        // The value is just another Adapter, and can be accessed using 'second'
+        const AdapterType &value = member.second;
+        if (value.maybeString()) {
+            cout << value.asString();
+        } else {
+            cout << maybeResolveRef(value, adapter);
+        }
+
+        cout << endl;
+    }
+}
+
+void usingJsonCppWithTemplateFn(const char *filename)
+{
+    rapidjson::Document document;
+    if (!valijson::utils::loadDocument(filename, document)) {
+        return;
+    }
+
+    valijson::adapters::RapidJsonAdapter adapter(document);
+    iterateJsonObject(adapter);
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        cerr << "Usage: " << endl;
+        cerr << "  " << argv[0] << " <filename>" << endl;
+        return 1;
+    }
+
+    // Load the document using jsoncpp and iterate over array using function template
+    cout << "-- Resolving JSON pointers using RapidJSON --" << endl;
+    usingJsonCppWithTemplateFn(argv[1]);
+    cout << endl;
+
+    return 0;
+}