11602105 C Lecture 12 Friends Exception Handling

8/14/2019 11602105 C Lecture 12 Friends Exception Handling

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Computer Programming II 1

Lecturer 12Lecturer 12

Friends andFriends andException HandlingException Handling
http://fit.mmu.edu.my/


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OutlinesOutlines

Friend relationshipFriend relationship Friend function

Friend method

Friend class

Exception HandlingException Handling Exception

Exception Handler try, throw and catch block


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3

Access Privileges - ReviewAccess Privileges - Review

(private, Public, protected)(private, Public, protected)

1. Public: methods of class itself, methods of derived

class, and other functions like main can access it.

2. Protected: methods of class itselfand methods of

derived class can access it.

3. Private: methods of class itselfcan access it.


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Will you be myWill you be my friend?friend?

Friend-ship allows a class to selectively grant access to its

private internals to other constructs.

C++ friends come in three flavors:friend functions

friend classesfriend methods (member functions)

Friend-ship is

A friend function can access both the private and protectedmembers of the class.


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FriendsFriends

function/method/classfunction/method/class Friend-ship allows a class to selectively grant access to its

private and protected internals to other function, method, and class.

C++ friends come in three flavors:friend functionsfriend classes friend methods (member functions)

- A friend functionis a function that can access private and

protected data members of a class, even though the function itself is

not a member of the class.- A friend classis a class whose functions can all access private and

protected data members ofanother class-A friend methodis a method that can access private and protected

data members of a class, even though the method itself is not a

member of the class.


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class Chong

{

public: Chong(); // constructor

friend void perform_sthg( );

...

};

void perform_sthg()

{ // can access private&Protected

data of //Chong

...

}

class Yin

{

public: Yin(); // constructor

int Yin_f1();

...

};

class Lim{ public:

Lim(); // constructor

friend int Yin::Yin_f1();

...

};

Only the member method Yin_f1 has

access to private&Protected data ofLim

The functionsperform_sthg has

access to private&Protected data of

Chong

// can access private&Protected

//data of Lim

Example: Friend Function / Method


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class Raj

{

public:Raj(); // constructor

int Raj_f1();

int Raj_f2();

int Raj_f3();

};

class Singh

{

public:

Singh(); // constructor

friend class Raj;

...

};

All member methods of

Raj (f1, f2, f3) have access to

Private&protected data of Singh

// can access private&Protected data

of Singh

Example: Friend Class
http://fit.mmu.edu.my/http://fit.mmu.edu.my/


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Friend Method


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Friend ClassFriendship is not

inherited, meaning that

classes derived from

YourOtherClass cannotaccess YourClass's

private members.

Friendship is not

transitive, so classes

that are friends of

YourOtherClass cannot

access YourClass's

private members.


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Exception HandlingException Handling


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Dealing with ErrorsDealing with Errors

When a program is executed, unexpected situation may occur. Such

a situation is called anexception

In other word: Exception is a run-time error caused by someabnormal condition

Example:

indexing outside the limits in an array division by zero failure of new to obtain a requested amount of memory

Exception handler

its a code to deal with these exceptions (run-time errors) when

they occured


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Exception Example

Division by zero

float x, y;

.y = 0.0;

float result = x/y

Index out of range

int array [10];

for (int i=0; i


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Three aspects of dealing with an error:

1. Identifying that an error has occurred

2. Handling (resolving) an identified error in order to eithercontinue execution of the program OR gracefullyterminate it.

3. If the error cannot be resolved at the current level of execution,communicate its existence to the next highest level of execution

Dealing with Errors

int main() {int x,y;

cout > x >> y;

cout


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Introduction to Exceptions

An exception is an object (int, char, text..etc) that containsinformation on an error and is used to communicate that

information to a higher level of execution.

The process of transferring an exception from its currentexecution context to the context above it is knows as

throwing an exception The point in the function code at which the exception isthrown is referred to as the throw point

An execution context that receives an exception and

accesses it is said to catch the exception


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The Syntax of Exceptions

C++ implements exceptions with three keywords

try, throw and catch

Try Block

- The code which mightgenerate a runtime error is writtenwithin the try block.

Format:

try {//Code that can generate exceptions

}


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The Syntax of Exceptions

Catch Block

- Catches the exception (errors) which is thrown by throwkeyword which is also generated from the code within the try

block. This is the exception handler.

Format: 5.catch() {error handling part:}

OR

2. catch () {error handling part; }


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# include

int main()

{ int value1, value2, result;

}// end of main

try

{ cin >> value1; cin >> value2;

}// end of try

catch (int a ){ cout


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Some times, we might have many different exceptions

1. We should write as many catch blocks.

2. This means also that we should have as many

throw statements.

3. BUT(usually), only one try.

But, which catch block will be instigated? (invoked)

The conflict will be eliminated depending on the parametersin the throw, i.e., OVERLOADING

The try-catch block

Th h bl k


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The try-catch blocktry {

// Code that could generate an exception }

catch () {

// Code that resolves a type1 exception

}

catch () {

// Code that resolves a type2 exception

}

catch () {

// Code that resolves a typeN exception

}; // end-of try-catch block


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The try-catch block


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Exception Matching

To catch every exception that is seen, use ellipsis.

catch () //This catches any exception

You can't tell what type of exception occurred

No argument to reference

Must always be placed as the last catch


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Exception Matching

catch()

{

cout


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Exception Matching

void main ( )

{

int a[10], n, I;

coutn:

func(n);for(I=0;I>a[I];

int sum=0;

for(I=0;I

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11602105 C Lecture 12 Friends Exception Handling