IN204 - Software Engineering - Object Oriented

IN204 - Software Engineering - Object Oriented
Programming
Tutorial 4 - Exceptions - October 21, 2016
B. Monsuez, F. Vedrine, A. Cutean, V. Paun
Preamble
You can find a reference guide on the IN204 course web page http://wwwdfr.ensta.fr/Cours/index.php?
usebdd=ensta&sigle=IN204&afficher=biblio
Exercise 1 Exception study
Create a project and execute the code below.
#include<iostream>
doubledivide(doublea,doubleb);
voidtest_divide();
voidtest_divide()
{
doublei,j;
for(;;){
std::cout<<"Lenumerateur(0pourarreter):";
std::cin>>i;
if(i==0)
break;
std::cout<<"Ledenominateur:";
std::cin>>j;
std::cout<<"Resultat:"<<divide(i,j)<<std::endl;
}
}
doubledivide(doublea,doubleb)
{
try{
if(!b)throwb;
}
catch(doubleb){
std::cout<<"Nepeutpasdiviserparzero.\n";
returnb;
}
returna/b;
}
Check behavior for the division by zero.
Question 2
The previous code corresponds to one of the two uses that satisfies the rules of exception management,
explain which rule is satisfied.
Now want it to satisfy the other of two rules, how can we modify the code to make it so?
Note: to revive an exception in a catch block just do
throw;
without any parameters.
Question 3.1
We are going to further refine and get it right this time. We want to define a class that derives from the
exception class std::exception found in the library
"Exception" .
This class will be called division_by_zero and will include implementing a counter for determining
the number of times that this class was caught by a catch block.
Naturally the division_by_zero class will derive from the class std::exception .
It is assumed that the method
void catched()
informs the object it was captured by a catch block.
And that the method
int getCount ()
provides the number of times the exception was caught by a catch block.
Define the class in question.
Question 3.2
Modify the previous code so that it is the exception represented by the division_by_zero class that is
raised.
Question 3.3
We wish to implement the following code:
voidtest_succesive_division()
{
doublei;
std::cout<<"Lenumerateur:";
std::cin>>i;
try{
successive_division(i);
}
catch(division_by_zeroe){
e.catched();
std::cout<<"Divisionparzeroauniveau"<<e.getCount()
<<std::endl;
}
}
doublesuccessive_division(doublei)
{
doublej;
std::cout<<"Ledenominateursuivant(-1pourarreter):";
std::cin>>j;
if(j==-1)
returni;
try{
successive_division(j);
returndivide(i,j);
}
catch(division_by_zeroe){
e.catched();
throwe;
}
}
Exercise 2 - Ensure that a certain code is always
executed, either if an exception occurs or not
In Java, you have the ability to write a finally block
try
{
…
}
finally
{
…
}
The code placed in the finally block is always executed, if an exception occurs or if no exception
occurs.
Question 1.1
In C++, this construction does not exist. Is is possible to ensure the same thing in C++ using catch
blocks?
Note: The instruction
try
{
…
}
catch(type1e)
{
//Capturelesexceptionsdérivantdetype1
}
catch(type1e)
{
//Capturelesexceptionsdérivantdetype2siellesn’ontpasétécapturéesparles
//exceptionsdetype1.
}
catch(…)
{
//Capturetouteslesexceptionsn’ayantpasétécapturéesparuneclauseprécédente
}
Question 1.2
We want the divide function defined in the previous question shows "function complete" at the end of
the function, and even if an exception was thrown.
How to deal with the solution proposed to the previous question?
What is the disadvantage of this approach?
2.1 Question
We suggest to circumvent the difficulty by using an object. We know that an object allocated on the stack is
systematically destroyed when exits its activation block.
When an object is destroyed, its destructor is called.
Note: In the destructor, it is possible to execute the code that would have been placed in the finally block of
JAVA that we wish to see systematically executed.
Complete the following class to display "function complete" when the object is destroyed.
classfinally
{
public:
finally(){}
~finally(){…}
…
}
Question 2.2
Implement this solution instead of the proposed solution to Question 1.2.
Check this solution is working properly.
Exercise 3 - Ensure that all exceptions are captured
Question 1
The exception division_by_zero may be raised by the divide function. Add this information to the
divide function.
Question 2
Compile your program.
What is happening then?
Review and correct your program based on the information present in the course.