rapidjson/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;

#if defined(__GNUC__)
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(effc++)
#endif

struct MessageHandler : public BaseReaderHandler<> {
	MessageHandler() : messages_(), state_(kExpectObjectStart), name_() {}

    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_;
};

#if defined(__GNUC__)
RAPIDJSON_DIAG_POP
#endif

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;
}