const declares immutable value void Test(char* t) { t++;// OK, address is not const t[0] = 'a'; // OK, char is not const } void Test2(const char* t) { t++;// OK, address is not const t[0] = 'a'; // NO, char is const } const Value

typedef char* PCHAR; void Test3(const PCHAR t) { t++;// NO, address is const t[0] = 'a'; // OK, char is not const } typedef const char* PCONSTCHAR; void Test4(PCONSTCHAR t) { t++;// OK, address is not const t[0] = 'a'; // NO, char is const } void Test5(const PCONSTCHAR t) { t++;// NO, address is const t[0] = 'a'; // NO, char is const } const Address

char myChar; char& myChar2 = myChar;// myChar2 points to myChar myChar = ‘a’;// Now myChar2 = ‘a’ myChar2 = ‘b’;// Now myChar = ‘b’ Reference is similar to pointer because it holds address internally Reference is different from pointer because you cannot manipulate (or see) the address Reference is an always-dereferenced pointer Reference cannot be NULL or invalid void Change (char& myChar) { myChar = ‘b’; } void main() { char myChar = ‘a’; Change(myChar);// Now myChar = ‘b’ } & Reference

References provide efficient means for quickly passing data to functions (i.e. the data is passed by address aka by reference). Const make the data you pass read-only to safeguard against accidental modifications. void Change (const char& myChar) { myChar = ‘b’;// No, char is const char tempChar = myChar; // OK, myChar is read-only } void main() { char myChar = ‘a’; Change(myChar);// Now myChar = ‘b’ } const Reference

class String { public: String(const String& aString);// Copy constructor void MakeUpper();// Modifies string to make it upper case int GetLength() const;// Retrieves string length without modifying it }; void Test(String myString)// We pass myString by value hence a copy constructor will be called {// and a new String instance will be constructed on stack myString.MakeUpper(); } void Test2(String& myString)// Copy constructor will be NOT called {// because myString is passed by reference myString.MakeUpper(); } void Test3(const String& myString)// Copy constructor will be NOT called {// because myString is passed by reference myString.MakeUpper();// NO, MakeUpper() modifies string but we pass it by const reference int length = myString.GetLength();// OK, GetLength() does not modify String (declared as const) } void main() { String myString(“some text”); Test(myString);// myString = “some text” because we passed it by value Test2(myString); // myString = “SOME TEXT” because we passed it by reference } const Reference (contd.)

class String { public: int GetLength() const// Instance method { int i; for ( i = 0; Buffer[i] != ‘\0’; i++);// OK, can refer to instance prop. Buffer return i; } static GetLength(const char* buffer) // Static method { int i; for ( i = 0; Buffer[i] != ‘\0’ && I < MaxLength; i++ );// NO, can not refer to instance property return i;// OK, can refer to static MaxLength property } private: const char* Buffer;// Instance property static int MaxLength;// Static property }; void main() { String::MaxLength = 10;// set static property String::GetLength(“some text”);// static method invocation String MyString1, MyString2;// Have the same MaxLength value } Static Members: Shared Among All Class Instances

class String { public: String();// Default constructor String(const char* buffer);// Init constructor public: // Does not encapsulate immutable char pointer const char* Buffer; }; void main() { String myString(“test”); myString.Buffer = “test2”;// We can change Buffer pointer } String Class: Quick char* Encapsulation

class String { public: String();// Default constructor String(const char* buffer);// Init constructor const char* GetBuffer() const;// Returns encapsulated buffer char operator [](int index) const;// Index operator to retrieve character String& operator = (const char* buffer);// Assignment operator to initialize private: // Encapsulated immutable char pointer const char* Buffer; }; void main() { String myString(“test”); myString.Buffer = “test2”;// NO, Buffer is private const char* p = myString.GetBuffer();// OK, get encapsulated buffer char c = myString[0];// Get 0-th character } String Class: Robust char* Encapsulation