Understanding Member Functions and Classes in C++

1. Department of Computer and Information Science,School of Science, IUPUI ClassesMember Qualifiers CSCI 240 Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

2. Member Functions -- Qualifiers  • inline Member Functions • Function Bodies are Substituted for the Function Call At Compile Time • All the Member Functions Defined within the Class Definition are Implicitly Inline • If Defined Outside the Class Definition, inline Qualifier is Required • Faster Execution • static Member Functions • Exist Before Any Class Instantiation -- Access Only the Static Class Members • const Member Functions • CANNOT Change Data Members • The ONLY ONE that can Process Constant Objects • Can also Process Non-Constant Objects

3. inline Member Functions -- Example • class student{ int ss, credits; public: int get_ss(){return ss;} //Implicitly "inline" inline int get_credits(); //Explicitly "inline" }; • //Explicitly "inline" int student::get_credits() {return credits;}

4. Nested Classes  • A Class Contained in Another Class • Multiple Levels of Nesting Are Allowed • Usual Scoping Rules Apply

5. Nested Classes -- Example • class one{ //Class "two" is nested inside the class "one" int a; public: class two{ int b; public: two(){b = 10;} void print_b() {cout << "two's b: " << b << endl;} }; two one_two; • one(){a = 100;} void print_a() {cout << "one's a: " << a << endl;} };

6. Nested Classes -- Example • main(){ one s1; //s1 is an object of "one" s1.print_a(); //a = 100 s1.one_two.print_b(); //b = 10 • //Object of class "two" defined inside "one" one::two s2; s2.print_b(); //b = 10 }

7. Constant Data Members • Principle of least privilege • Only give objects permissions they need, no more • Keyword const • Specify that an object is not modifiable • Any attempt to modify the object is a syntax error • Example const Time noon( 12, 0, 0 ); • Declares a const object noon of class Time and initializes it to 12

8. Constant Member Functions • const objects require const functions • Member functions declared const cannot modify their object • const must be specified in function prototype and definition • Prototype: ReturnType FunctionName(param1,param2…) const; • Definition: ReturnType FunctionName(param1,param2…) const { …} • Example: int A::getValue() const { return privateDataMember }; • Returns the value of a data member but doesn’t modify anything so is declared const • Constructors / Destructors cannot be const • They need to initialize variables, therefore modifying them

9. Constant Members and Functions • Member initializer syntax • All data members can be initialized using member initializer syntax • constructor for Increment is modified as follows: Increment::Increment( int c, int i ) : increment( i ) { count = c; } • : increment( i ) initializes increment to i • consts and references must be initialized using member initializer syntax • Multiple member initializers • Use comma-separated list after the colon

10. const -- Example  • class student{ int ss, credits; public: student():ss(0), credits(0){} //const member function cannot modify the data member int get_ss() const {return ss;} int get_credits(){return credits;} }; • main(){ student s1; const student s2; s1.get_ss(); s1.get_credits(); s2.get_ss(); //constant object s2.get_credits(); //ERROR!!! Cannot call a non-constant function }

11. Acknowledgements • These slides were originally prepared by Rajeev Raje, modified by Dale Roberts.