Exception handling in c programming

ALGORITHMS AND COMPUTING ( LAB )
END SEMESTER PRESENTATIONS
GROUP C

PRESENTATION CONTENTS
• Team/Topic Introduction
• Errors & its Types
• Exception Handling Basics
• Occurrence & Handling of an Exception ( Flow diagrams )
• Methods to handle an Exception
• Example Program 1 ( DL 1)
• Causes of Exception Occurrence
• Grading
• Q/A Session

GROUP MEMBERS:
• Raza Najam
• Hassaan Idrees
• Waleed Raza
• Syed Ahmed Fuad
• Tanveer Hussain
• Hassan Qamar Rana

Hassaan • Exception Handling Basics
Raza • Methods to handle an Exception
Fuad • Example Program 1 ( DL 1)
Tanveer • Causes of Exception Occurrence
Waleed • Example Program 2 ( DL 2)
Raza
• Grading
• Q/A Session

ERRORS AND ITS TYPES

• There are three basic types of errors:
1- Syntax Error
2- Semantic Errors
3- Logical Errors
These errors are detected by the ‘C’ compiler

• There are also a few kinds of errors in ‘C’ those are not detected by the
compiler.
4- Run Time Errors
5- Compile Time Errors
These error are not identified by the compiler and so they are termed
as “EXCEPTIONS”

WHAT IS REALLY AN EXCEPTION?
• An exception is an indication of a problem that occurs during a program’s
execution.
• Exception is a runtime problem that occurs rarely
handling an exception allows programs to continue executing as if no
problem had been encountered.
• Helps terminating the program in a controlled manner rather in an
unpredictable fashion
• Exception handling enables programmers to create applications that can
resolve (or handle) exceptions.

DIFFERENCES BETWEEN AN ERROR AND AN EXCEPTION
1- Errors occur at compilation time as well as run time while exceptions
mostly occur at run time.
2- Compile time errors are detected by the compiler while exceptions need
to be predicted by the programmer himself
3- Errors occur frequently while exceptions, as the name suggests occur
seldom
4- Error detection and debugging is easier while exception prediction and
its handling is a bit complex procedure
5- Errors can be removed by removing syntax and logical mistakes while
exception handling needs pre-defined or user defined procedures.

BENEFITS:
• Helps improve a program's fault tolerance.
• Enables the programmer to remove error-handling code from the ‘main
line’ of the program’s execution
• Programmers can decide to handle any exceptions they choose – all
exceptions of a certain type or all exceptions of a group of related types

EXCEPTION HANDLING IN C
• C does not provide direct support for error/exception handling.
• By convention, the programmer is expected to develop an algorithm for
an error and exception case free program.
• Intelligent visualization skills and prediction of end-user actions on a
particular event prevents errors from occurring in the first place.
• The programmer is expected to test return values from a function.

Exception handling is designed to:
Process synchronous errors, which occur when a statement executes.
Common examples of these errors are:
1. out-of-range array subscripts
2. arithmetic overflow
3. division by zero
4. invalid function parameters
5. unsuccessful memory allocation, due to lack of memory
Exception handling is not designed to:
Process errors associated with asynchronous events fro example:
1. Disk I/O completions
2. Network message arrivals
3. Mouse-clicks and keystrokes
which occur in parallel with, and independent of, the program’s flow
control.

HOW TO HANDLE AN EXCEPTION:
- Ignore the exception
(Non – Professional )
- Abort the program
( Even Worst )
- Set error indicators
( Beginner’s Approach )
- Issue an error-message and call exit().
( Non – Feasible )
- Use setjmp() and longjmp()
( Leading to Professional)

THE CLASSIC ‘C’ APPROACH TO EXCEPTION HANDLING.
• Each function returns a value indicating success or failure.
• Every function must check the return code of every function call it
makes and take care of errors.
• Exceptions make it easy to separate error handling from the rest of
the code.
• Exceptions make it easy to separate error handling from the rest of
the code.
• Intermediate functions can completely ignore errors occurring in
functions they call, if they can't handle them anyway

Main body
{
Any program…

Program Pauses and control is
Exception Occurs shifted to some other function

Further program

End of program Now the user defined function
decides what to do with that
particular exception
}

METHODS OF EXCEPTION HANDLING

There are two methods to handle an exception in C.
1- if - else method
2- setjmp() and longjmp() method


1- if - else method
• Exception is handled by making decisions via if – else.
• Occurrence of an exception is checked by the return
values of a function or by defined parameters.
• Along with that condition is placed an if – else statement
that checks and performs the respective action against
that exception.

1- if - else method
main()
{
code…
code…
EXCEPTION
if (n==exception condition)
printf(“Operation cannot be performed”);
/*here we have to decide whether to exit the program or to
ignore the exception and run the program anyway */
else
continue
code…
}

2- setjmp () and longjmp() method:
• setjmp() and longjmp() are used to jump away from a
particular location in a program into another function.
• The programmer written code, inside that function
handles the exception
• To test the occurrence of an exception the setjmp()
function is called up.
• setjmp() saves the most recent event of the program
before that statement in a buffer called jmp_buf.

2- setjmp () and longjmp() method:
• As soon as the exception test is complete the setjmp()
returns a value to the function.
• If the value returned from the setjmp() to the longjmp()
is ‘0’ it means that there was an exception condition.
• Now the program will again start from the same point
where it stopped (saved in the buffer), until the exception
condition is removed or repaired.
• On the other hand programmer can also display error
messages or other fool-proof techniques.

• Exception Handling Basics
• Methods to handle an Exception
• Programs Difficulty Level 1
• Causes of Exception Occurrence
• Grading
• Q/A Session

PROGRAM DIFFICULTY LEVEL 1

PROGRAM 1:

#include <stdio.h>
void main (void)
{
int a , b , c ;
a=1;
b=0;
c=a/b
printf(“%d”,c);
}

#include <stdio.h> /* for fprintf and stderr */
#include <stdlib.h> /* for exit */ PROGRAM 2
int main( void ) DL 1
{
float dividend = 50;
float divisor ;
float quotient;

printf("Enter a divisor for a dividend of 50nn");
scanf("%f", &divisor);
if (divisor == 0)
{
/* Example handling of this error. Writing a message to stderr, and
* exiting with failure.
*/
fprintf(stderr, "nnDivision by zero !!! Aborting... ={ nn");
exit(EXIT_FAILURE); /* indicate failure.*/
}

quotient = (dividend/divisor);
printf("n%.2fnn",quotient);
exit(EXIT_SUCCESS); /* indicate success.*/
}

#include <setjmp.h>
#include <stdio.h> PROGRAM 3
#include <stdlib.h>
void main(void)
DL 1
{
float dividend = 50;
float divisor ;
float quotient;
jmp_buf env;

printf("Enter a divisor for a dividend of 50nn");
setjump(env); Stores the scanf() statement in a buffer
scanf("%f", &divisor);

if (divisor == 0) Exceptional Case
longjmp(env,2); Throws back to where we paused

quotient = (dividend/divisor);
printf("n%.2fnn",quotient);
exit(EXIT_SUCCESS); /* indicate success.*/

return 0;
}

CAUSES OF EXCEPTION HANDLING
Exception Class Cause
ArgumentException An argument to a method was invalid.
A null argument was passed to a method that
ArgumentNullException
doesn't accept it.
ArgumentOutOfRangeException Argument value is out of range.
ArithmeticException Arithmetic over - or underflow has occurred.
Attempt to store the wrong type of object in an
ArrayTypeMismatchException
array.
DivideByZeroException An attempt was made to divide by zero.
FormatException The format of an argument is wrong.
NotFiniteNumberException A number is not valid.
NullReferenceException Attempt to use an unassigned reference.
OutOfMemoryException Not enough memory to continue execution.

#include <stdio.h> /* fprintf */
#include <errno.h> /* errno */ PROGRAM 1
#include <stdlib.h>
#include <string.h>
/* malloc, free, exit */
/* strerror */
DL 2
extern int errno;
int main( void )
{
/* pointer to char, requesting dynamic allocation of 2,000,000,000
* storage elements (declared as an integer constant of type
* unsigned long int). (If your system has less than 2GB of memory
* available, then this call to malloc will fail)
*/
char *ptr = malloc( 2000000000 );

if ( ptr == NULL )
puts("malloc failed");
else
{
/* the rest of the code hereafter can assume that 2,000,000,000
* chars were successfully allocated...
*/
free( ptr );
}

exit(EXIT_SUCCESS); /* exiting program */
}

GROUP C GRADING
Group leader: Raza Najam

Members Name Searching Teamwork PPT Skills Willing to C Presentation Skills Total/10
10 10 10 10 10 5
Hassaan Idrees 8 8 7 7 8 3.8
Syed Ahmed Fuad 8 8 5 9 7 3.7
Tanveer Hussain 8 8 5 6 5 3.2
Waleed Raza 7 7 5 5 4 2.8
Hasan Qamar - - - - - -

Exception handling in c programming

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