add a new query function

api/http/cpp/src/GstoreConnector.cpp

@@ -166,6 +166,14 @@ GstoreConnector::query(string username, string password, string db_name, string
 	return recv_msg;
 }
 
+void GstoreConnector::query(string username, string password, string db_name, string sparql, string filename)
+{
+    string url = "http://" + this->serverIP + ":" + std::to_string(this->serverPort);
+    string cmd = url + "/?operation=query&username=" + username + "&password=" + password + "&db_name=" + db_name + "&format=json&sparql=" + sparql;
+    int ret = hc.Get(cmd, filename, true);
+    return;
+}
+
 string
 GstoreConnector::show()
 {

api/http/cpp/src/GstoreConnector.h

@@ -31,6 +31,7 @@ public:
 	bool build(std::string _db_name, std::string _rdf_file_path, std::string username, std::string password);
 	bool drop(std::string _db_name);
 	std::string query(std::string username, std::string password, std::string db_name, std::string sparql);
+    void query(std::string username, std::string password, std::string db_name, std::string sparql, std::string filename);
     std::string show();  //show all databases
 	std::string user(std::string type, std::string username1, std::string password1, std::string username2, std::string addtion);
 	std::string showUser();