All notes


JSON (JavaScript Object Notation). See

JSON values can be:

// JSON object. NOTE: json has no syntax for comments!
{"firstName":"John", "lastName":"Doe"}

// JSON array
    {"firstName":"John", "lastName":"Doe"}, 
    {"firstName":"Anna", "lastName":"Smith"}, 

In javascript, it is

var employees = [
    {"firstName":"John", "lastName":"Doe"},
    {"firstName":"Anna", "lastName":"Smith"},
    {"firstName":"Peter","lastName": "Jones"}



int ParseJsonFromString()
	const char* str = "{\"uploadid\": \"UP000000\",\"code\": 100,\"msg\": \"\",\"files\": \"\"}";
	Json::Reader reader;
	Json::Value root;
	if (reader.parse(str, root))  // reader将Json字符串解析到root,root将包含Json里所有子元素
		std::string upload_id = root["uploadid"].asString();  // 访问节点,upload_id = "UP000000"
		int code = root["code"].asInt();    // 访问节点,code = 100
	return 0;

Example from jsoncpp refman

// Configuration options
    // Default encoding for text
    "encoding" : "UTF-8",
    // Plug-ins loaded at start-up
    "plug-ins" : [
    // Tab indent size
    "indent" : { "length" : 3, "use_space": true }
jsoncpp supports comments as meta-data.

Json::Value root;   // will contains the root value after parsing.
Json::Reader reader;
bool parsingSuccessful = reader.parse( config_doc, root );
if ( !parsingSuccessful ) {
    // report to the user the failure and their locations in the document.
    std::cout  << "Failed to parse configuration\n"
               << reader.getFormattedErrorMessages();
// Get the value of the member of root named 'encoding', return 'UTF-8' if there is no such member.
std::string encoding = root.get("encoding", "UTF-8" ).asString();
// Get the value of the member of root named 'encoding', return a 'null' value if there is no such member.
const Json::Value plugins = root["plug-ins"];
for ( int index = 0; index < plugins.size(); ++index )  // Iterates over the sequence elements.
	loadPlugIn( plugins[index].asString() );

setIndentLength( root["indent"].get("length", 3).asInt() );
setIndentUseSpace( root["indent"].get("use_space", true).asBool() );

// At application shutdown to make the new configuration document:
// Since Json::Value has implicit constructor for all value types, it is not
// necessary to explicitly construct the Json::Value object:
root["encoding"] = getCurrentEncoding();
root["indent"]["length"] = getCurrentIndentLength();
root["indent"]["use_space"] = getCurrentIndentUseSpace();

Json::StyledWriter writer;
// Make a new JSON document for the configuration. Preserve original comments.
std::string outputConfig = writer.write( root );

// You can also use streams.  This will put the contents of any JSON
// stream at a particular sub-value, if you'd like.
std::cin >> root["subtree"];

// And you can write to a stream, using the StyledWriter automatically.
std::cout << root;