Lecture 1 Try Throw Catch.pptx

DISCOVER . LEARN . EMPOWER
Topic: Try, Throw, Catch
INSTITUTE - UIE
DEPARTMENT- ACADEMIC UNIT-2
Bachelor of Engineering (Computer Science & Engineering)
Subject Name: Object Oriented Programming using C++
Code:20CST151
Unit-3

Object Oriented
Programming
using C++
Course Objectives
2
• To enable the students to understand various stages and constructs
of C++ programming language and relate them to engineering
programming problems.
• To improve their ability to analyze and address variety of problems in
programming domains.

3
CO
Number
Title Level
CO1 Provide the environment that allows students to
understand object-oriented programming Concepts.
Understand
CO2 Demonstrate basic experimental skills for differentiating
between object-oriented and procedural programming
paradigms and the advantages of object-oriented
programs.
Remember
CO3 Demonstrate their coding skill on complex programming
concepts and use it for generating solutions for
engineering and mathematical problems.
Understand
CO4 Develop skills to understand the application of classes,
objects, constructors, destructors, inheritance, operator
overloading and polymorphism, pointers, virtual
functions, exception handling, file operations and
handling.
Understand
Course Outcomes

Scheme of Evaluation
4
Sr.
No.
Type of Assessment
Task
Weightage of actual
conduct
Frequency of Task Final Weightage in Internal
Assessment (Prorated
Marks)
Remarks
1. Assignment* 10 marks of
each assignment
One Per Unit 10 marks As applicable to
course types depicted
above.
2. Time Bound
Surprise
Test
12 marks for each
test
One per Unit 4 marks As applicable to
course types
depicted above.
3. Quiz 4 marks of each quiz 2 per Unit 4marks As applicable to
course types
depicted above.
4. Mid-Semester Test** 20 marks for one
MST.
2 per semester 20 marks As applicable to
course types
depicted above.
5. Presentation*** Non Graded: Engagement
Task
Only for Self Study
MNGCourses.
6. Homework NA One per lecture topic
(of 2
questions)
Non-Graded: Engagement
Task
As applicable to
course types
depicted above.
7. Discussion Forum NA One per
Chapter
Non Graded: Engagement
Task
As applicable to
course types depicted
above.
8. Attendance and
Engagement Score
on BB
NA NA 2 marks

• What is an Exception
• Exception Handler Try, Throw,
Catch
5
CONTENTS

WHAT IS AN EXCEPTION?
• An exception is a problem that arises during the execution of a
program. A C++ exception is a response to an exceptional
circumstance that arises while a program is running, such as an
attempt to divide by zero.
• Exceptions are different, however. You can't eliminate exceptional
circumstances; you can only prepare for them. Your users will run out
of memory from time to time, and the only question is what you will
do. Your choices are limited to these:
Crash the program.
Inform the user and exit gracefully.
Inform the user and allow the user to try to recover and continue.
Take corrective action and continue without disturbing the user.
6

WHAT IS AN EXCEPTION?
• Many kinds of errors can cause exceptions--problems ranging from serious hardware errors, such as a hard disk
crash, to simple programming errors, such as trying to access an out-of-bounds array element.
• When such an error occurs, the method creates an exception object and hands it off to the runtime system.
• The exception object contains information about the exception, including its type and the state of the program
when the error occurred.
• The runtime system is then responsible for finding some code to handle the error.
• In programming terminology, creating an exception object and handing it to the runtime system is called
throwing an exception.
7

EXCEPTION HANDLER
• After a method throws an exception, the runtime system leaps into action to find someone to handle the exception.
• The set of possible "someones" to handle the exception is the set of methods in the call stack of the method where the error occurred.
• The runtime system searches backwards through the call stack, beginning with the method in which the error occurred, until it finds a
method that contains an appropriate exception handler.
• An exception handler is considered appropriate if the type of the exception thrown is the same as the type of exception handled by the
handler.
• Thus the exception bubbles up through the call stack until an appropriate handler is found and one of the calling methods handles the
exception.
• The exception handler chosen is said to catch the exception.
8

EXCEPTION HANDLING
9
Figure 1: Syntax
• Errors disrupt normal execution of a program. Exception handling is very necessary, and it is the process of handling errors or exceptions.
It makes sure that the execution of the program is not affected by the exceptions and slowly handles them without causing any issue to
the program execution.
• In C++, exception handling is provided by using three constructs or keywords; namely, try, catch and throw.
• Block of code that provides a way to handle the exception is called “exception handler”.

Exception Handling Advantages
• It helps the programmer to write robust and fault-tolerant programs that can deal with problems continue executing or terminate
gracefully.
• Exception handling also is useful for processing problems that occur when a program interacts with software elements, such as member
functions, constructors, destructors and classes.
10

Exception Handling Mechanism
• Error handling code basically consists of two parts.
Detect error and throw the exception (in try block)
Catch exception and take appropriate action. (in catch block)
• Steps to be followed are:
1. Find the problem (Hit the exception).
2. Inform that error has occurred (throw the exception).
3. Receive the error information (catch the exception).
4. Take corrective actions (handle the exception).
11

• Exception handling basically has 3 keywords:
1. Try
2. Throw
3. Catch
• In try block, we add those blocks of statements which may generate exceptions.
When an exception is detected, it is thrown using a throw statement in a try block.
• A catch block defined by keyword catch ‘catches’ the exception ‘thrown’ by throw
statement in the try block and handles it appropriately.
• The catch block that catches an exception must immediately follows the try block that
throws the exception.
12

13
Figure 2: Depiction of try catch block

26-09-2022
• The throw statement is almost similar to function call. The only difference is that
instead of calling the function, it calls the catch block.
• In this sense, the catch block is like function definition with a parameter that
matches the type of value being thrown.
• The throw expression accepts one parameter as its argument and this is passed to
the exception handler.
• You can have a number of throw statements at different parts of your try block
with different values being thrown so that the exception handler on receiving the
parameter will know what restorative actions to take.
4
Throw and Catch

26-09-2022
• The exception handler can be identified by the keyword catch .
• catch always takes only one parameter.
• The type of the catch parameter is important as the type of the argument passed by
the throw expression is checked against it and the catch function with the correct
parameter type is executed.
• This way we can chain multiple exception handlers and only the one with the
correct parameter type gets executed.
5
Throw and Catch

26-09-2022 5
Throw and Catch
try
{ // code
if ( x )
throw 10;
// code
if (y)
throw 20;
//code
}
try { // code here }
catch (int param) {
cout << "int exception";
}
catch (char param) {
cout << "char exception";
}
catch (...) {
cout << "default exception";
}

26-09-2022 6
Throwing an Exception in a Function

Applications
• Helps in finding and handling run-time anomalies or abnormal
conditions that a program encounters during its execution.
20

21
Summary
In this lecture we have
discussed about Exception
Handling.
We have discussed some
examples of try throw catch
blocks
Moreover, we have learnt
about how to use exception
handling in functions

Frequently Asked question
Q1 What should I catch?
Answer: In keeping with the C++ tradition of “there’s more than one way to do that” (translation: “give programmers options and
tradeoffs so they can decide what’s best for them in their situation”), C++ allows you a variety of options for catching.
You can catch by value.
You can catch by reference.
You can catch by pointer.
In fact, you have all the flexibility that you have in declaring function parameters, and the rules for whether a particular exception
matches (i.e., will be caught by) a particular catch clause are almost exactly the same as the rules for parameter compatibility when
calling a function.
Q2 What should I throw?
Answer: C++, unlike just about every other language with exceptions, is very accomodating when it comes to what you can throw. In
fact, you can throw anything you like. That begs the question then, what should you throw?
Generally, it’s best to throw objects, not built-ins. If possible, you should throw instances of classes that derive (ultimately) from the
std::exception class. By making your exception class inherit (ultimately) from the standard exception base-class, you are making life
easier for your users (they have the option of catching most things via std::exception), plus you are probably providing them with
more information (such as the fact that your particular exception might be a refinement of std::runtime_error or whatever).
22

Assessment Questions:
23
1. By default, what a program does when it detects an exception?
a) Continue running
b) Results in the termination of the program
c) Calls other functions of the program
d) Removes the exception and tells the programmer about an exception
2. Why do we need to handle exceptions?
a) To avoid unexpected behaviour of a program during run-time
b) To let compiler remove all exceptions by itself
c) To successfully compile the program
d) To get correct output
3. How Exception handling is implemented in the C++ program?
a) Using Exception keyword
b) Using try-catch block
c) Using Exception block
d) Using Error handling schedules

Discussion forum.
What are the various C++ Standard Exceptions?
24

REFERENCES
TEXT BOOKS
T1 E Balagurusamy., “Object Oriented Programming in C++”, Tata McGraw-Hill.
T2 Robert Lafore, “Object Oriented Programming in C++”, Waite Group.
REFERENCE BOOKS
R1 Herbert Schildt , “C++- The Complete Reference”, Tata McGraw-Hill 2003, New
Delhi.
R2 Bjarne Stroustrup: “The C++ Programming Language” (4th Edition). Addison-Wesley.
R3 Ravichandran , “Programming with C++”,Tata McGraw-Hill Education.
R4 Joyce M. Farrell,” Object Oriented Programming Using C++”, Learning.
R5 Programming Languages: Design and Implementation (4th Edition), by Terrence W.
Pratt, Marvin V. Zelkowitz, Pearson.
R6 Programming Language Pragmatics, Third Edition, by Michael L. Scott, Morgan
Kaufmann.
Websites:
1. https://www.sanfoundry.com/cplusplus-programming-questions-answers-exception-handling-1/
2. https://www.tutorialspoint.com/cplusplus/cpp_exceptions_handling.htm
3. https://www.geeksforgeeks.org/exception-handling-c/
25

Lecture 1 Try Throw Catch.pptx

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