Lecture7-ExceptionsLecture7-Exceptions_.ppt

Exception
• An exception is a unusual, often
unpredictable event, detectable by
software or hardware, that requires
special processing occurring at runtime
• In C++, a variable or class object that
represents an exceptional event.

Handling Exception
• If without handling,
• Program crashes
• Falls into unknown state
• An exception handler is a section of
program code that is designed to execute
when a particular exception occurs
• Resolve the exception
• Lead to known state, such as exiting
the program

Standard Exceptions
 Exceptions Thrown by the Language
– new
 Exceptions Thrown by Standard
Library Routines
 Exceptions Thrown by user code,
using throw statement

The throw Statement
Throw: to signal the fact that an
exception has occurred; also called
raise
ThrowStatement throw Expression

The try-catch Statement
try
Block
catch (FormalParameter)
Block
catch (FormalParameter)
TryCatchStatement
How one part of the program catches and processes
the exception that another part of the program throws.
FormalParameter
DataType VariableName
…

Execution of try-catch
No
statements throw
an exception
Statement
following entire try-catch
statement
A
statement throws
an exception
Exception
Handler
Statements to deal with exception are executed
Control moves
directly to exception
handler

Example of a try-catch Statement
try
{
// Statements that process personnel data and may throw
// exceptions of type int, string, and SalaryError
}
catch ( int )
{
// Statements to handle an int exception
}
catch ( string s )
{
cout << s << endl; // Prints "Invalid customer age"
// More statements to handle an age error
}
catch ( SalaryError )
{
// Statements to handle a salary error
}

int main()
{ int a,b;
cout<<"Enter the values of a and b n";
cin>>a;
cin>>b;
int x=a-b;
try
{
if(x!=0)
cout<<"Result(a/x) = "<<a/x <<endl;
else
{
throw(x);
}
}catch(int i)
{
cout<<"Exception caught :"<<x<<endl;
}
cout<<"nEND";
return 0;
}
Enter the values of a
and b
10
10
Exception caught :0
END
Enter the values of a
and b
10
5
Result(a/x) = 2
END

int main()
{ int a,b;
cout<<"Enter the values of a and b n";
cin>>a;
cin>>b;
int x=a-b;
try
{ try
{ if(x!=0)
cout<<"Result(a/x) = "<<a/x <<endl;
else
{
throw(x);
}
}catch(int i)
{ cout<<"Exception caught :"<<x<<endl;
throw;
}
} catch(...)
{
cout<<"Caught rethrown exceptionn";
}
cout<<"nEND";
return 0;
}
Enter the values
of a and b
10
10
Exception
caught :0
Caught rethrown
exception
END

Throwing an Exception to be
Caught by the Calling Code
void Func4()
{
if ( error )
throw ErrType();
}
Normal
return
void Func3()
{
try
{
Func4();
}
catch ( ErrType )
{
}
}
Function
call
Return from
thrown
exception

#include <iostream>
using namespace std;
void divide(int x, int y, int z)
{
cout<<"n Inside Functionn";
if((x-y)!=0)
{
int r=z/(x-y);
cout<<"n Result :"<<r<<endl;
}
else
{
throw(x-y);
}
}
int main()
{
cout<<"Inside Main"<<endl;
try
{
divide(10,20,30);
divide(10,10,20);
}
catch(int i)
{
cout<<"Exception
caught :"<<i<<endl;
}
return 0;
}
Inside Main
Inside Function
Result :-3
Inside Function
Exception caught :0

#include <iostream>
using namespace std;
void test(int x)
{
try
{
if(x==1) throw x;
else if(x==0) throw 'x';
else if(x==-1) throw 1.0;
cout<<"nend of try block"<<endl;
}catch(char c){
cout<<"Caught a character"<<endl;
} catch(int m)
{ cout<<"Caught an
integer"<<endl;
} catch(double d)
{ cout<<"Caught a double"<<endl;
} cout<<"End of try-catch segmentn
n";
}
int main()
{
cout<<"Testing Multiple catches";
cout<<"x==1 n";
test(1);
cout<<"x==0 n";
test(0);
cout<<"x==-1 n";
test(-1);
cout<<"x==2 n";
test(2);
return 0;
}

Testing Multiple
catchesx==1
Caught an integer
End of try-catch segment
x==0
Caught a character
x==-1
Caught a double
x==2
end of try block

// quotient.cpp -- Quotient program
#include<iostream.h>
#include <string.h>
int Quotient( int, int );
class DivByZero {}; // Exception class
int main()
{
int numer; // Numerator
int denom; // Denominator
//read in numerator
and denominator
while(cin)
{
try
{
cout << "Their quotient: "
<< Quotient(numer,denom) <<endl;
}
catch ( DivByZero )//exception handler
{
cout<<“Denominator can't be 0"<< endl;
}
// read in numerator and denominator
}
return 0;
}

 An exception is a unusual, often unpredictable event that
requires special processing occurring at runtime
– throw
– try-catch

Lecture7-ExceptionsLecture7-Exceptions_.ppt

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