1. C++ Class Members Class Definition class Name { public: constructor(s)
destructor
function members
data members
protected:
private: };
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2. C++ Class Members Class Definition - Data Members Data Members
It is important to note …..
Each class instance gets distinct copies of all data members
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3. C++ Class Members Class Definition - Data Members class MyClass {
public:
MyClass() { myValue = 10; }
int getMyValue () { return myValue;}
int setMyValue (int aValue) { myValue = aValue;}
private:
int myValue; };
int main(void)
MyClass inst0, inst1;
inst1.setMyValue(20);
cout << inst0.getMyValue() << endl
<< inst1.getMyValue() << endl;
return 0; }
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4. C++ Class Members Class Definition - Function Members Function Members
Unlike data members
Only one instance of each function member exists for a class
Unless the function is declared inline
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5. C++ Class Members Class Definition - Function Members Function Members
If only a single instance…..
How are data members which function manipulates
bound to the function instance?????
What is not shown
The member function has a hidden argument
The arg is a pointer to the object that was sent the message
Pointer is identified by the keyword this
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6. C++ Class Members Class Definition - Function Members Function Members
The this pointer
Has type ClassType
Contains the address of the class instance through which the member function was invoked
Starting address is same as the address of the first variable in the class structure
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7. C++ Class Members Class Definition - Function Members Function Members
Every nonstatic function member has a pointer implicitly declared
ClassName * const this;
this is initialized to point to the object for which the member
function was invoked
Because this is declared const
It cannot be changed
Object pointed to can
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8. C++ Class Members Class Definition - Function Members Function Members
Since this is a pointer to the beginning of the class structure
One can select elements using pointer notation
this -> myElement
To refer to the entire instance…..
*this
return *this
Will produce a copy of the instance as the return value
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9. C++ Class Members Class Definition - Function Members class Link {
public:
void append (Link* aLink);
void setPrev (Link* aLink);
private:
Link* next;
Link* prev; };
void Link :: append(Link* aLink)
next = aLink;
aLink -> setPrev(this);
return; }
Next Li
Li+1
Previous
this
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10. C++ Class Members Managing Storage - Object Creation
When a C++ object is created 2 events occur……..
Storage is allocated for the object
The constructor is called to initialize the storage
Storage allocation occurs in several ways and at different times
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11. C++ Class Members Managing Storage - Object Creation Static Storage
Allocated when the program begins
Constant for the life of the program
Stack
Storage allocated on the stack when an execution point is
reached - Opening curly brace.
Released at the complementary execution point - closing curly
brace.
Heap - Free Store
Storage is dynamically allocated from the heap at runtime
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12. C++ Class Members Managing Storage - Object Creation Declaration
Introduces a name
Tells the compiler what the name means
Usually go into header files
Definition
Allocates storage for the name
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13. C++ Class Members Managing Storage - Object Creation Variable
The compiler determines the variable size and generates space
If there is an initializing value, the value entered into that storage
Compile time storage usually allocated at the opening brace
Constructor not called until sequence point where object defined
Auto storage will be allocated on the stack
Function
Compiler generates code and allocates storage to hold the code
Storage for function has an address that can be produced using
Function name with no arg list
Address of operator
Usually go into implementation files
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14. C++ Class Members Managing Storage - Linkage Linkage
Describes storage to represent an identifier as seen by linker
Internal
Storage created for identifier for file being compiled
Name may be used in other files without conflict
External
Single piece of storage for all files being compiled
Accessed from other files by keyword extern
Variables defined outside functions
Inline function definitions default to external linkage
Automatic (local) Variables
Exist on the stack while function being called
Auto variables have no linkage
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15. C++ Class Members Managing Storage - Inline Functions Inline Functions
C++ permits specification of inline functions
Identified by keyword inline … the definition of function follows
syntax
inline type functionName (argsi) { body }
When inline definition encountered
No code generated
Code remembered and substituted for each function call
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16. C++ Class Members Static Data Members
A class is a type not a data object
When an instance of a class is defined…..
The instance gets a copy of all data members
If data member declared static
Single copy
Shared by all instances of the class
Smalltalk
Pool variables
class M
char a
static int b m0
char a m1 m2 m3
int b
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17. C++ Class Members Static Data Members syntax Declaration
static type varName;
Definition
type ClassName :: varName < = value >
Static member exists even if no class instances exist
Remain in scope of class
Can only be accessed from outside if declared public
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18. C++ Class Members Static Data Members Storage for a static variable
Must be explicitly reserved and initialized
Static can be declared within a class
Definition and initialization must occur outside Class
Can be only single definition
Static (nonclass) variables
Initialized to 0 by default
Static class variables
Cannot be initialized by the constructor
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19. C++ Class Members Initializing Static Data Members...
class SimpleClass {
public:
SimpleClass () {}
SimpleClass (int aValue){myValue = aValue;}
// static char myChar = 'c'; This is illegal
static char myChar;
private:
static int myValue; };
// Define and initialize the static variables
int SimpleClass::myValue = 10;
char SimpleClass::myChar = 'a';
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20. C++ Class Members Static Data Members Static Data Member
Can appear as a default arg to a member function
Non-static Data Member
Cannot appear as a default arg to a member function
Within a class body…..
int a;
static int b;
int f1 ( int myValue0 = a ); // illegal
int f2 ( int myValue1 = b ); // ok
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21. C++ Class Members Static Data Members
A static data member can be an instance of the class of which it is a
member…..
A non-static can only point to an instance of it’s class.
Within a class body
class F1 {
public:
F1 *a; // ok
static F1 b; // ok
F1 c; // illegal };
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22. C++ Class Members Const Data Members
Class data members can be specified as const
Consequence
Storage always allocated and must be initialized at point of
definition
Initialization must occur in the constructor
Implemented via the initialization list
Storage not allocated until instance created…...
At that time, the const must be
Created
Initialized
Const variable persists for the lifetime of the instance
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23. C++ Class Members Static Function Members
Function members can be declared static
A static function has no this pointer
static function can access
Directly
static members
enums and typedefs
Indirectly
Regular members via . or -> through an explicit object
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24. C++ Class Members Static Function Members class SimpleClass { public:
//static int getMyNumber() {return myNumber;} requires an object
static int getMyNumber() { return myValue;}
static int getMyStuff(SimpleClass *myClass) {return myClass->myNumber;}
static int getMyVal() {return myValue;}
static char myChar;
char myLetter;
private:
static int myValue;
int myNumber; };
int SimpleClass::myValue=10;
char SimpleClass::myChar = 'a';
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25. C++ Class Members Static Function Members int main() {
SimpleClass myClass, yourClass, *myClassPtr = &myClass ;
cout << SimpleClass::getMyStuff(myClassPtr) << endl;
cout << myClass.myChar << " " << SimpleClass::myChar << endl;
return 0; }
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26. C++ Class Members Const Function Members
The keyword const can be placed after argument list of member
function
syntax
returnType functionName ( argsi ) const { function body }
Tells compiler that function
Can only read data members
Cannot write them
Member functions declared const
Can be called for non-const objects
Non-const member functions
Cannot be called for const objects.
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27. C++ Class Members Overloading Function Members
Functions can use same name in the same scope
If signature is unique
Name plus signature
Uniquely identify function
Same holds true for member functions
Same rules applied to disambiguate
Must provide Implementation for each overloaded function
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28. C++ Class Members Operator Function Members
C++ defined operators can be overloaded to work on Class type
operands
Must take at least one class type argument
syntax
operator X (args) { body }
X is the operator symbol being overloaded
args - as appropriate for implementation
body - implements the function
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29. C++ Class Members Operator Function Members Invocation
Assume + is overloaded
Infix expression syntax
A + B
A, B can be member or non-member instances
Function call syntax
A.operator+ (B)
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30. C++ Class Members Operator Function Members Rules
Because operator functions are invoked using the same syntax
Operator functions...
1. Must have the same number of arguments as language defined versions
2. Must have the same precedence as the builtin operators…This cannot be overridden
3. Cannot have default parameters
4. Cannot override the predefined meaning
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31. C++ Class Members Operator Function Members Limitations
Because of the operator function syntax
1. Certain user defined operators cannot behave
analogously to built in versions
Prefix version
operator++ () {}
Postfix version
operator++ (int) {}
Some operators cannot be overloaded. , ?: :: . *
Some operators must be members only =, [ ] , ( ), ->
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32. C++ Class Members Overloading Operators class Complex { public:
int im, re;
Complex(int r=0, int i=0):re(r), im(i) { }
Complex operator+ (Complex a1) {return Complex(re+a1.re, im+a1.im);}
Complex& operator++ ()
re += 1, im += 1;
cout << “prefix" << endl;
return Complex(re -1, im -1); }
Complex& operator++ (int)
re+=1, im+=1;
cout << "postfix" << endl;
return *this; };
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33. C++ Class Members Operator Function Members Member
Left hand operand must be an instance of class overloading
the operator
Unary
x is class instance
Binary
x.operator(y)
x y
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34. C++ Class Members Operator Function Members Non-Member
If operator requires left hand operand of a different type…..
Must use non-member syntax
Must be declared friend if the operator requires access to
protected or private members
Unary
Binary
x y
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35. C++ Class Members Operators in Action
The Copy Constructor and the Assignment Operator
There are many occasions when a copy of an object is needed
Object passed by value
x.func(y)
A copy of y is made and passed
Object returned by value
Object initialized by another object
ClassName x1 = x2
A copy of x2 is made
Object assigned to another object
x1 = x2
x2 is copied to x1 and
x1 is destroyed
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36. C++ Class Members Operators in Action The Copy Constructor
A constructor that…..
Takes a reference to an object of the same class as an
argument
Performs initialization on newly created objects
Used by compiler to copy objects by value
syntax
class X ( const class X& )
class X ( class X& )
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37. C++ Class Members Operators in Action The Copy Constructor
If a copy constructor is not defined
Shallow bitwise copy performed - memcpy
If a copied object uses new to allocate memory when created
One must write a copy constructor
Copy constructor need only be written
If class object is passed by value
To prevent pass by value
Define a private copy constructor
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38. C++ Class Members Operators in Action
The Assignment Operator - operator=()
Called when one initialized object is to be assigned to a second.
The operator must serve as a destructor to the assignee object.
Can have a return value…
The most common is *this
Is not called for the declarations such as
ClassName object1 = object2
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39. C++ Class Members Class Members - Friends A class Definition….
Provides 3 levels of access to data and function members
public
protected
private
Closed
Open
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40. C++ Class Members Class Members - Friends
C++ provides means for more liberal access to non-public members
under specified set of conditions…..
Nonmember designated as a friend of the class
Class friend is designated by
Keyword friend
Followed by class name
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41. C++ Class Members Class Members - Friends
Once an object is designated as a friend….
It has access to non-public members as if they were public
If B is designated as friend of A
B can access A’s non-public members
A cannot access B’s
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42. C++ Class Members Class Members - Friends Friend may be: 1. Class
friend class X;
2. A particular function
friend int sub (int y);
3. A particular class member
friend int Mult::get();
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43. C++ Class Members Class Members - Friends
A friend does not have a this pointer unless it is a member function in
its own right
Question:
If it is a member function which this pointer does it have
Class A a;
Class B b;
Let B be declared as a friend of A
The this pointer of a function bFunct() contains
the address of the class instance b
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44. C++ Class Members Class Members - Friends Caveats and Problems,,,
Friends can have access to everything … this defeats data
hiding.
Introduces extra coupling between classes.
Permits change of internal state from the outside.
Should use member functions not friends to change state.
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