Exception Handling

popo

2

Exception HandlingTwo types of bugs (errors)Logical errorSyntactic error

Logical error occur due to poor understanding of the problem and solution procedure

Syntactic error occur due to poor understanding of language , can solve by compiler

popo

3

Exception HandlingExceptions are runtime errorsSuch as division by zero, array out of bounds, no

disk space, trying to read/write data from improper address (or an unopened file)…

When a run time error encountered the program terminates

C++ provides built in features to detect & handle exceptions

popo

4

Exception HandlingExceptions are 2 typesSynchronous exceptionsAsynchronous exceptions

Synchronous out of range index, overflow, divide by zero..

Asynchronous beyond the control of the program such as keyboard problem….

Exception handling mechanism mainly for Synchronous errors

popo

5

Exception HandlingException handling mechanism detect and report

an runtime error, so appropriate action can be taken

Exception handling mechanism steps1) Find an error (hit exception)2) Inform that an error occurred (throw exception)3) Receive the error information (catch exception)4) Take corrective action(handle exception)

popo

6

Exception HandlingException handling code consists of the following

segments To detect errorTo throw errorTo catch errorTo take appropriate action

popo

7

Exception HandlingException handling mechanism done with three

keywordstrythrowcatchtry blockA block of statements surrounded with braces, which

may generate errorIf you suspect a statement or a set of statements may

cause any runtime error, group them in a block and name it as try

popo

8

Exception Handlingtry{

statements;}throwWhen an error is detected in the try block it is thrown using a throw statement in the

try blocktry{

int a,b;……if(a==0){

throw “Divide by Zero”;}cout<<“checking”;

}

popo

9

Exception Handling• main()• {• cout << "Start\n";• try { // start a try block• cout << "Inside try block\n";• throw (100); // throw an error• cout << "This will not execute";• }• catch (int i) { // catch an error• cout << "Caught an exception -- value is: ";• cout << i << "\n";• }• cout << "End“;• This program displays the following output:• Start• Inside try block• Caught an exception -- value is: 100• End

popo

10

Exception HandlingcatchDefined by the keyword catch Catches the exception thrown by the throw statement in the try blockThe catch block that catches an exception must immediately follow the try blockAny thrown exception must be caught by a catch statement that has thrown the exceptiontry{

int a,b;……if(a==0){throw “Divide by Zero”;}cout<<“checking”;

}catch (type arguments){

statments}

popo

11

Exception HandlingWhen try block throws an exception the program

control leaves the try block and enteres the catch statements

Exceptions are objects used to transmit information about a problem

If the type object throw matches the argument type in the catch , then catch block is executed for handling the error

If they do not matches program terminates

popo

12

Exception HandlingVoid main(){

int a,b,c;cout<<“enter 2 nos “;cin>>a>>b;try{

if(b!=0){

c=a/b;cout<<c;}else{

throw(b); //throw int object}

}catch(int x) // catches the exception{

cout<<“exception caught “ <<x;}

Cout<<“END”;}

popo

13

Exception HandlingException handling in functionVoid check(int x,int y){

if(y!=0){

int z=x/y;cout<<z;}else{

throw(y);}

}Void main(){

try{

check(3,0);}catch(int z){

cout<<“Caught the exception”;}cout<<“END”getch();

}

popo

14

Exception Handling

popo

15

Exception Handling• Using Multiple catch Statements• As stated, you can have more than one catch associated with a try. • In fact, it is common to do so. • However, each catch must catch a different type of exception. • For example, this program catches both integers and strings.• try• {

if(test) throw test;else throw "Value is zero";

• }• catch(int i) • {

cout << "Caught Exception #: " << i << '\n';• }• catch(const char *str) • {

cout << "Caught a string: ";cout << str << '\n';

• }• Each catch statement responds only to its own type.

16

Exception Handling• Catching All Exceptions• In some circumstances you will want an exception

handler to catch all exceptions• This is easy to accomplish. • Simply use this form of catch.• catch(...) • {

// process all exceptions• }

popo

17

Exception Handling• try• {

if(test==0) throw test; // throw intif(test==1) throw 'a'; // throw charif(test==2) throw 123.23; // throw double

• }• catch(...) { // catch all exceptions• cout << "Caught One!\n";• }

popo