Fixed broken const-correctness in dbc.hpp and dbc.cpp.

Author: SimonCahill

include/libdbc/dbc.hpp

@@ -27,18 +27,18 @@ class DbcParser : public Parser {
 	void parse_file(const std::string& file_name) override;
 	void parse_file(std::istream& stream) override;
 
-	std::string get_version() const;
-	std::vector<std::string> get_nodes() const;
-	std::vector<Libdbc::Message> get_messages() const;
+	const std::string& get_version() const;
+	const std::vector<std::string>& get_nodes() const;
+	const std::vector<Libdbc::Message>& get_messages() const;
 
 	Message::ParseSignalsStatus parse_message(uint32_t message_id, const std::vector<uint8_t>& data, std::vector<double>& out_values);
 
-	std::vector<std::string> unused_lines() const;
+	const std::vector<std::string>& unused_lines() const;
 
 private:
-	std::string version;
-	std::vector<std::string> nodes;
-	std::vector<Libdbc::Message> messages;
+	std::string version{};
+	std::vector<std::string> nodes{};
+	std::vector<Libdbc::Message> messages{};
 
 	std::regex version_re;
 	std::regex bit_timing_re;
@@ -48,7 +48,7 @@ class DbcParser : public Parser {
 	std::regex value_re;
 	std::regex signal_re;
 
-	std::vector<std::string> missed_lines;
+	std::vector<std::string> missed_lines{};
 
 	void parse_dbc_header(std::istream& file_stream);
 	void parse_dbc_nodes(std::istream& file_stream);

src/dbc.cpp

@@ -107,15 +107,15 @@ std::string DbcParser::get_extension(const std::string& file_name) {
 	return "";
 }
 
-std::string DbcParser::get_version() const {
+const std::string& DbcParser::get_version() const {
 	return version;
 }
 
-std::vector<std::string> DbcParser::get_nodes() const {
+const std::vector<std::string>& DbcParser::get_nodes() const {
 	return nodes;
 }
 
-std::vector<Libdbc::Message> DbcParser::get_messages() const {
+const std::vector<Libdbc::Message>& DbcParser::get_messages() const {
 	return messages;
 }
 
@@ -246,7 +246,7 @@ void DbcParser::parse_dbc_messages(const std::vector<std::string>& lines) {
 	}
 }
 
-std::vector<std::string> DbcParser::unused_lines() const {
+const std::vector<std::string>& DbcParser::unused_lines() const {
 	return missed_lines;
 }