diff --git a/src/asmexception.h b/src/asmexception.h
index 7789a9f..6e4ceef 100644
--- a/src/asmexception.h
+++ b/src/asmexception.h
@@ -81,7 +81,7 @@ class AsmException_FileError : public AsmException
 class AsmException_FileError_##a : public AsmException_FileError			\
 {																			\
 public:																		\
-	explicit AsmException_FileError_##a( const std::string filename )			\
+	explicit AsmException_FileError_##a( const std::string& filename )		\
 		:	AsmException_FileError( filename ) {}							\
 																			\
 	virtual ~AsmException_FileError_##a() {}								\
@@ -120,13 +120,13 @@ class AsmException_SyntaxError : public AsmException
 	{
 	}
 
-	AsmException_SyntaxError( std::string line, int column )
+	AsmException_SyntaxError( const std::string& line, int column )
 		:	m_line( line ),
 			m_column( column )
 	{
 	}
 
-	AsmException_SyntaxError( std::string line, int column, std::string extra )
+	AsmException_SyntaxError( const std::string& line, int column, const std::string& extra )
 		:	m_line( line ),
 			m_column( column ),
 			m_extra( extra )
@@ -161,7 +161,7 @@ class AsmException_SyntaxError : public AsmException
 class AsmException_SyntaxError_##a : public AsmException_SyntaxError		\
 {																			\
 public:																		\
-	AsmException_SyntaxError_##a( std::string line, int column )			\
+	AsmException_SyntaxError_##a( const std::string& line, int column )		\
 		:	AsmException_SyntaxError( line, column ) {}						\
 																			\
 	virtual ~AsmException_SyntaxError_##a() {}								\
@@ -174,7 +174,7 @@ public:																		\
 class AsmException_SyntaxError_##a : public AsmException_SyntaxError		\
 {																			\
 public:																		\
-	AsmException_SyntaxError_##a( std::string line, int column, std::string extra )			\
+	AsmException_SyntaxError_##a( const std::string& line, int column, const std::string& extra )	\
 		:	AsmException_SyntaxError( line, column, extra ) {}				\
 																			\
 	virtual ~AsmException_SyntaxError_##a() {}								\
@@ -270,7 +270,7 @@ class AsmException_AssembleError : public AsmException_SyntaxError
 
 	virtual ~AsmException_AssembleError() {}
 
-	void SetString( std::string line )			{ m_line = line; }
+	void SetString( const std::string& line )	{ m_line = line; }
 	void SetColumn( int column )				{ m_column = column; }
 
 	virtual const char* Message() const
@@ -309,7 +309,7 @@ class AsmException_UserError : public AsmException_SyntaxError
 {
 public:
 
-	AsmException_UserError( std::string line, int column, std::string message )
+	AsmException_UserError( const std::string& line, int column, const std::string& message )
 		:	AsmException_SyntaxError( line, column ),
 			m_message( message )
 	{
diff --git a/src/commands.cpp b/src/commands.cpp
index bb3bd0f..42a8b8c 100644
--- a/src/commands.cpp
+++ b/src/commands.cpp
@@ -164,21 +164,17 @@ template<class T> class Argument
 		// No value was available (i.e. the end of the parameters)
 		StateMissing
 	};
-	Argument(string line, int column, State state) :
+	Argument(const string& line, int column, State state) :
 		m_line(line), m_column(column), m_state(state)
 	{
 	}
-	Argument(string line, int column, T value) :
+	Argument(const string& line, int column, const T& value) :
 		m_line(line), m_column(column), m_state(StateFound), m_value(value)
 	{
 	}
 	Argument(const Argument<T>& that) :
 		m_line(that.m_line), m_column(that.m_column), m_state(that.m_state), m_value(that.m_value)
 	{
-		m_line = that.m_line;
-		m_column = that.m_column;
-		m_state = that.m_state;
-		m_value = that.m_value;
 	}
 	// Is a value available?
 	bool Found() const
@@ -226,7 +222,7 @@ template<class T> class Argument
 	}
 	// Set a default value for optional parameters.
 	// This is overloaded for strings below.
-	Argument<T>& Default(T value)
+	Argument<T>& Default(const T& value)
 	{
 		if ( !Found() )
 		{
@@ -265,7 +261,7 @@ typedef Argument<double> DoubleArg;
 typedef Argument<string> StringArg;
 typedef Argument<Value> ValueArg;
 
-template<> StringArg& StringArg::Default(string value)
+template<> StringArg& StringArg::Default(const string& value)
 {
 	if ( !Found() )
 	{
@@ -1218,12 +1214,12 @@ void LineParser::HandleSave()
 
 			if ( !objFile )
 			{
-				throw AsmException_FileError_OpenObj( saveFile.c_str() );
+				throw AsmException_FileError_OpenObj( saveFile );
 			}
 
 			if ( !objFile.write( reinterpret_cast< const char* >( ObjectCode::Instance().GetAddr( start ) ), end - start ) )
 			{
-				throw AsmException_FileError_WriteObj( saveFile.c_str() );
+				throw AsmException_FileError_WriteObj( saveFile );
 			}
 
 			objFile.close();
diff --git a/src/lineparser.cpp b/src/lineparser.cpp
index 59a7859..05494ed 100644
--- a/src/lineparser.cpp
+++ b/src/lineparser.cpp
@@ -42,7 +42,7 @@ using namespace std;
 	Constructor for LineParser
 */
 /*************************************************************************************************/
-LineParser::LineParser( SourceCode* sourceCode, string line )
+LineParser::LineParser( SourceCode* sourceCode, const string& line )
 	:	m_sourceCode( sourceCode ),
 		m_line( line ),
 		m_column( 0 )
@@ -76,7 +76,7 @@ LineParser::~LineParser()
 	Process one line of the file
 */
 /*************************************************************************************************/
-void LineParser::Process( string line )
+void LineParser::Process( const string& line )
 {
 	m_line = line;
 	m_column = 0;
diff --git a/src/lineparser.h b/src/lineparser.h
index 78fbc1d..e1c0d0e 100644
--- a/src/lineparser.h
+++ b/src/lineparser.h
@@ -34,13 +34,13 @@ class LineParser
 
 	// Constructor/destructor
 
-	LineParser( SourceCode* sourceCode, std::string line );
+	LineParser( SourceCode* sourceCode, const std::string& line );
 	LineParser( SourceCode* sourceCode );
 	~LineParser();
 
 	// Process the given line
 
-	void Process( std::string line );
+	void Process( const std::string& line );
 
 	// Accessors
 
diff --git a/src/sourcecode.cpp b/src/sourcecode.cpp
index 0d21496..0647c6f 100644
--- a/src/sourcecode.cpp
+++ b/src/sourcecode.cpp
@@ -582,7 +582,7 @@ bool SourceCode::IsRealForLevel( int level ) const
 	Search up the stack for a value for a symbol.  N.B. This is dynamic scoping.
 */
 /*************************************************************************************************/
-bool SourceCode::GetSymbolValue(std::string name, Value& value)
+bool SourceCode::GetSymbolValue(const std::string& name, Value& value)
 {
 	for ( int forLevel = GetForLevel(); forLevel >= 0; forLevel-- )
 	{
diff --git a/src/sourcecode.h b/src/sourcecode.h
index 433ac15..d453fea 100644
--- a/src/sourcecode.h
+++ b/src/sourcecode.h
@@ -121,7 +121,7 @@ class SourceCode
 	inline int 				GetInitialForStackPtr() const { return m_initialForStackPtr; }
 	inline Macro*			GetCurrentMacro() { return m_currentMacro; }
 
-	bool					GetSymbolValue(std::string name, Value& value);
+	bool					GetSymbolValue(const std::string& name, Value& value);
 	ScopedSymbolName		GetScopedSymbolName( const std::string& symbolName, int level = -1 ) const;
 
 	bool					ShouldOutputAsm();
diff --git a/src/sourcefile.cpp b/src/sourcefile.cpp
index fa9d012..09bc3df 100644
--- a/src/sourcefile.cpp
+++ b/src/sourcefile.cpp
@@ -48,7 +48,7 @@ using namespace std;
 	The supplied file will be opened.  If there is a problem, an AsmException will be thrown.
 */
 /*************************************************************************************************/
-static string ReadFile( string filename )
+static string ReadFile( const string& filename )
 {
 	// we have to open in binary, due to a bug in MinGW which means that calling
 	// tellg() on a text-mode file ruins the file pointer!