Add messagereader example

example/messagereader/messagereader.cpp

+// Reading a message JSON with Reader (SAX-style API).
+// The JSON should be an object with key-string pairs.
+
+#include "rapidjson/reader.h"
+#include "rapidjson/error/en.h"
+#include <iostream>
+#include <string>
+#include <map>
+
+using namespace std;
+using namespace rapidjson;
+
+typedef map<string, string> MessageMap;
+
+struct MessageHandler : public BaseReaderHandler<> {
+    MessageHandler() : state_(kExpectObjectStart) {}
+
+    bool StartObject() {
+		switch (state_) {
+		case kExpectObjectStart:
+			state_ = kExpectNameOrObjectEnd;
+			return true;
+		default:
+			return false;
+		}
+    }
+
+    bool String(const char* str, SizeType length, bool) {
+		switch (state_) {
+		case kExpectNameOrObjectEnd:
+            name_ = string(str, length);
+			state_ = kExpectValue;
+			return true;
+		case kExpectValue:
+			messages_.insert(MessageMap::value_type(name_, string(str, length)));
+			state_ = kExpectNameOrObjectEnd;
+			return true;
+		default:
+			return false;
+		}
+    }
+
+    bool EndObject(SizeType) { return state_ == kExpectNameOrObjectEnd; }
+
+	bool Default() { return false; } // All other events are invalid.
+
+	MessageMap messages_;
+    enum State {
+        kExpectObjectStart,
+        kExpectNameOrObjectEnd,
+        kExpectValue,
+    }state_;
+    std::string name_;
+};
+
+void ParseMessages(const char* json, MessageMap& messages) {
+    Reader reader;
+    MessageHandler handler;
+    StringStream ss(json);
+	if (reader.Parse(ss, handler))
+		messages.swap(handler.messages_);	// Only change it if success.
+	else {
+		ParseErrorCode e = reader.GetParseErrorCode();
+		size_t o = reader.GetErrorOffset();
+		cout << "Error: " << GetParseError_En(e) << endl;;
+		cout << " at offset " << o << " near '" << string(json).substr(o, 10) << "...'" << endl;
+	}
+}
+
+int main() {
+    MessageMap messages;
+
+	const char* json1 = "{ \"greeting\" : \"Hello!\", \"farewell\" : \"bye-bye!\" }";
+	cout << json1 << endl;
+    ParseMessages(json1, messages);
+
+    for (MessageMap::const_iterator itr = messages.begin(); itr != messages.end(); ++itr)
+        cout << itr->first << ": " << itr->second << endl;
+
+	cout << endl << "Parse a JSON with invalid schema." << endl;
+	const char* json2 = "{ \"greeting\" : \"Hello!\", \"farewell\" : \"bye-bye!\", \"foo\" : {} }";
+	cout << json2 << endl;
+	ParseMessages(json2, messages);
+
+    return 0;
+}