Functions & Constructor http://ecomputernotes.com

Review Class Concept Definition Data members Member Functions Access specifier http://ecomputernotes.com

Member Functions Member functions are the functions that operate on the data encapsulated in the class Public member functions are the interface to the class http://ecomputernotes.com

Member Functions (contd.) Define member function inside the class definition OR Define member function outside the class definition But they must be declared inside class definition http://ecomputernotes.com

Function Inside Class Body class ClassName { … public: ReturnType FunctionName() { … } }; http://ecomputernotes.com

Example Define a class of student that has a roll number. This class should have a function that can be used to set the roll number http://ecomputernotes.com

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

Function Outside Class Body class ClassName{ … public: ReturnType FunctionName(); }; ReturnType ClassName::FunctionName() { … }

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

Inline Functions Instead of calling an inline function compiler replaces the code at the function call point Keyword ‘inline’ is used to request compiler to make a function inline It is a request and not a command http://ecomputernotes.com

Example inline int Area(int len, int hi) { return len * hi; } int main() { cout << Area(10,20); } http://ecomputernotes.com

Inline Functions If we define the function inside the class body then the function is by default an inline function In case function is defined outside the class body then we must use the keyword ‘inline’ to make a function inline http://ecomputernotes.com

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

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

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

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

Constructor http://ecomputernotes.com

Constructor Constructor is used to initialize the objects of a class Constructor is used to ensure that object is in well defined state at the time of creation Constructor is automatically called when the object is created Constructor are not usually called explicitly http://ecomputernotes.com

Constructor (contd.) Constructor is a special function having same name as the class name Constructor does not have return type Constructors are commonly public members http://ecomputernotes.com

Example class Student{ … public: Student(){ rollNo = 0; … } }; http://ecomputernotes.com

Example int main() { Student aStudent; /*constructor is implicitly called at this point*/ } http://ecomputernotes.com

Default Constructor Constructor without any argument is called default constructor If we do not define a default constructor the compiler will generate a default constructor This compiler generated default constructor initialize the data members to their default values http://ecomputernotes.com

Example class Student { int rollNo; char *name; float GPA; public: … //no constructors }; http://ecomputernotes.com

Example Compiler generated default constructor { rollNo = 0; GPA = 0.0; name = NULL; } http://ecomputernotes.com

Constructor Overloading Constructors can have parameters These parameters are used to initialize the data members with user supplied data http://ecomputernotes.com

Example class Student{ … public: Student(); Student(char * aName); Student(char * aName, int aRollNo); Student(int aRollNo, int aRollNo, float aGPA); }; http://ecomputernotes.com

Example Student::Student(int aRollNo, char * aName){ if(aRollNo < 0){ rollNo = 0; } else { rollNo = aRollNo; } … } http://ecomputernotes.com

Example int main() { Student student1; Student student2(“Name”); Student student3(”Name”, 1); Student student4(”Name”,1,4.0); } http://ecomputernotes.com

Constructor Overloading Use default parameter value to reduce the writing effort http://ecomputernotes.com

Example Student::Student( char * aName = NULL, int aRollNo= 0, float aGPA = 0.0){ … } Is equivalent to Student(); Student(char * aName); Student(char * aName, int aRollNo); Student(char * Name, int aRollNo, float aGPA); 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; Student studentB = studentA; func1(studentA); } http://ecomputernotes.com

Copy Constructor (Syntax) 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; Student studentB = studentA;

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

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

Example Student studentA; Student studentB = studentA;