Exceptions

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Contents

Definition
Try, Catch, Throw
Standard Exceptions
Page Comments

Key Facts

Gyroscopic Couple: The rate of change of angular momentum ( $\inline \tau$ ) = $\inline I\omega\Omega$ (In the limit).

$\inline I$ = Moment of Inertia.
$\inline \omega$ = Angular velocity
$\inline \Omega$ = Angular velocity of precession.

Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.

Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.

Definition

Exceptions occur because of problems arising at runtime (memory overflow, data outside the prescribed limits) and provide a way to react to exceptional circumstances.

Try, Catch, Throw

try {
   // code that could throw an exception
}
[ catch (exception-declaration) {
   // code that executes when exception-declaration is thrown
   // in the try block
}
[catch (exception-declaration) {
   // code that handles another exception type
} ] . . . ]
// The following syntax shows a throw expression:
throw [expression]

The try, throw, and catch statements implement exception handling.

The code after the try clause is the guarded section of code. The throw expression raises an exception. The code block after the catch clause is the exception handler, and handles the exception thrown by the throw expression. The exception-declaration statement indicates the type of exception the clause handles. The type can be any valid data type, including a C++ class.

The operand of throw is syntactically similar to the operand of a return statement.

Standard Exceptions

The C++ Standard library provides a base class named exception specifically designed to declare objects to be thrown as exceptions, which is defined in the <exception> header file under the namespace std.

Exception	Description
`bad_alloc`	thrown by new on allocation failure
`bad_cast`	thrown by dynamic_cast when fails with a referenced type
`bad_exception`	thrown when an exception type doesn't match any catch
`bad_typeid`	thrown by typeid
`ios_base::failure`	thrown by functions in the iostream library

References

Example:

Example - nested try-catch

Problem

This simple program illustrates 2 nested try-catch.

Workings

#include <iostream>
#include <conio.h>
 
using namespace std;
 
int main()
{
  try
   {
      try
      {
         throw 5;
      }
      catch(int e)
      {
	 throw 10;
      }
   }
   catch(int e)
   {
      cout <<"Exception "<<e<<"."<<endl;
   }
 
  _getch();
  return 0;
}

Solution

Output:

Exception 10.