Never return a handle to a data member You are never sure that function accessing the reference will not change the value of the variable

Never return a handle to a data member You are never sure that function accessing the reference will not change the value of the variable

Never return a handle to a data member You are never sure that function accessing the reference will not change the value of the variable

Constructor http://ecomputernotes.com

Review Member functions implementation Constructors Constructors overloading Copy constructors http://ecomputernotes.com

Copy Constructor Copy constructor are used when: Initializing an object at the time of creation When an object is passed by value to a function http://ecomputernotes.com

Example void func1(Student student){ … } int main(){ Student studentA(“Ahmad”); Student studentB = studentA; func1(studentA); } http://ecomputernotes.com

Copy Constructor (contd.) Student::Student( const Student &obj){ rollNo = obj.rollNo; name = obj.name; GPA = obj.GPA; } http://ecomputernotes.com

Shallow Copy When we initialize one object with another then the compiler copies state of one object to the other This kind of copying is called shallow copying http://ecomputernotes.com

Example Student studentA(“Ahmad”); Student studentB = studentA; http://ecomputernotes.com

Example int main(){ Student studentA(“Ahmad”,1); { Student studentB = studentA; http://ecomputernotes.com

Example int main(){ Student studentA(“Ahmad”,1); { Student studentB = studentA; } } http://ecomputernotes.com

Copy Constructor (contd.) Student::Student( const Student & obj){ int len = strlen(obj.name); name = new char[len+1] strcpy(name, obj.name); … /*copy rest of the data members*/ } http://ecomputernotes.com

Example int main(){ Student studentA(“Ahmad”,1); { Student studentB = studentA;

Example int main(){ Student studentA(“Ahmad”,1); { Student studentB = studentA; } } http://ecomputernotes.com

Copy Constructor (contd.) Copy constructor is normally used to perform deep copy If we do not make a copy constructor then the compiler performs shallow copy http://ecomputernotes.com

Destructor Destructor is used to free memory that is allocated through dynamic allocation Destructor is used to perform house keeping operations http://ecomputernotes.com

Destructor (contd.) Destructor is a function with the same name as that of class, but preceded with a tilde ‘~’ http://ecomputernotes.com

Example class Student { … public: ~Student(){ if(name){ delete []name; } } } http://ecomputernotes.com

Overloading Destructors cannot be overloaded http://ecomputernotes.com

Sequence of Calls Constructors and destructors are called automatically Constructors are called in the sequence in which object is declared Destructors are called in reverse order http://ecomputernotes.com

Example Student::Student(char * aName){ … cout << aName << “Cons\n”; } Student::~Student(){ cout << name << “Dest\n”; } }; http://ecomputernotes.com

Example int main() { Student studentB(“Ali”); Student studentA(“Ahmad”); return 0; } http://ecomputernotes.com

Example Output: Ali Cons Ahmad Cons Ahmad Dest Ali Dest http://ecomputernotes.com

Accessor Functions Usually the data member are defined in private part of a class – information hiding Accessor functions are functions that are used to access these private data members Accessor functions also useful in reducing error

Example – Accessing Data Member class Student{ … int rollNo; public: void setRollNo(int aRollNo){ rollNo = aRollNo; } }; http://ecomputernotes.com

Example – Avoiding Error void Student::setRollNo(int aRollNo){ if(aRollNo < 0){ rollNo = 0; } else { rollNo = aRollNo; } } http://ecomputernotes.com

Example - Getter class Student{ … int rollNo; public: int getRollNo(){ return rollNo; } }; http://ecomputernotes.com

this Pointer class Student{ int rollNo; char *name; float GPA; public: int getRollNo(); void setRollNo(int aRollNo); … }; http://ecomputernotes.com

this Pointer The compiler reserves space for the functions defined in the class Space for data is not allocated (since no object is yet created) Function Space getRollNo(), … http://ecomputernotes.com

this Pointer Student s1, s2, s3;

this Pointer Function space is common for every variable Whenever a new object is created: Memory is reserved for variables only Previously defined functions are used over and over again http://ecomputernotes.com

this Pointer Memory layout for objects created: How does the functions know on which object to act?

this Pointer Address of each object is passed to the calling function This address is deferenced by the functions and hence they act on correct objects The variable containing the “self-address” is called this pointer

Passing this Pointer Whenever a function is called the this pointer is passed as a parameter to that function Function with n parameters is actually called with n+1 parameters http://ecomputernotes.com

Example void Student::setName(char *) is internally represented as void Student::setName(char *, const Student *) http://ecomputernotes.com

Declaration of this DataType * const this; http://ecomputernotes.com

Compiler Generated Code Student::Student(){ rollNo = 0; } Student::Student(){ this->rollNo = 0; } http://ecomputernotes.com