Exception handling

Exception are type of error
Let's quickly brush up the concept of error.
Errors are the mistake made by the programmer.
Error are of two type:
- Syntactic error: example - missing of semicolon, colon, brackets, etc. Basically where we are using wrong syntax.
- Logical error: example - using wrong formula for calculation.
Now all those error which are run time error like dividing by zero, accessing value at wrong index of array comes under exception.

Now let's discuss exception handling ↓

Exception handling is a much elegant solution as compared to other error handling mechanisms (handling through if-else blocks).
- It enables separation of main logic and error handling code.
Exception handling provide a systematic, object-oriented approach to handling erros generated by C++ classes.
For example:
- running out of memory
- not being able to open a file
- or using out-of-bound index

Exception handling process

Programmer writes the code that is suspected to cause an exception in try block.
Code section that encounters an error throws an object that is used to represent exception.
Catch block follow try block to catch the object thrown.

Syntax - Throw

The keyword throw is used to throw an exception.
Any expression can be used to represent the exception that has occured

                    
throw n;
throw (n);

Syntax - Try and Catch

                    
int main()
{
    try{
        ... 
    }
    catch(Exception1 obj)
    {
        ...
    }
    catch(Exception2 obj)
    {
        ...
    }
    return 0;
}

Catch blocks

Catch handler must be preceded by a try block or any other catch handler.
Catch handlers are only executed when an exception has occured.
The catch blocks are tried in order they are written.

Let's understand with program

Program which divide two number:
- We know that if divisor is zero, this will cause exception.
First we will see program without using exceptional handling ↓

                   
#include <iostream>
using namespace std;

int main()
{
    int a, b, r;
    cout << "Enter the value of a : ";
    cin >> a;
    cout << "Enter the value of b : ";
    cin >> b;
    if (b != 0)
        r = a / b;
    else
    {
        cout << "Cannot divide by zero";
    }

    return 0;
}

Output ↓

                
Enter the value of a : 12
Enter the value of b : 0
Cannot divide by zero

Now we will implement it using try and catch block

                   
#include <iostream>
using namespace std;

int main()
{
    int a, b;
    float r;
    cout << "Enter the value of a : ";
    cin >> a;
    try
    {
        cout << "Enter the value of b : ";
        cin >> b;
        if (b == 0)
            throw 0;
        r = a / b;
        cout << "The result if : " << r << endl;
    }
    catch (int)
    {
        cout << "cannot divide by zero" << endl;
    }
    return 0;
}

Output ↓

                
Enter the value of a : 14
Enter the value of b : 0
cannot divide by zero

                
Enter the value of a : 15
Enter the value of b : 3
The result is : 5

Reference ↓