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

What is Exception Handling?

In C++, exception handling is the process of dealing with runtime errors. We handle exceptions so that the application’s normal flow can be maintained even when runtime errors occur.

The exceptions can be broadly categorized into two types:

• Compile Time
• Run Time

Exception handling in C++ is based on three keywords: try, catch, and throw.

try block:

A try block identifies a section of code for which specific exceptions will be raised. It is immediately followed by one or more catch blocks.

catch block:

A program catches an exception with an exception handler at the point in the program where the problem should be handled. The catch block is designed to catch errors and handle exceptions. Multiple catch blocks can be used to handle different types of exceptions and perform different actions when they occur.

throw:

When a problem occurs, a program throws an exception. This is accomplished with the throw keyword. A throw expression takes one parameter, which is passed to the handler.

Syntax:

try
{
    //code
    throw parameter;
}
catch(exceptionname ex)
{
    //code to handle exception
}

Why Exception Handling? 

Exception handling has the following major advantages over traditional error handling:

• Error Handling code separated from Normal Code Functions/Methods
• Can handle only the exceptions they choose
• Classification of Error Types

Example: code without exception handling

#include <iostream>
using namespace std;

double division(int a, int b) {
   return (a/b);
}

int main () {
   int x = 50;
   int y = 0;
   double z = 0;
 
   
      z = division(x, y);
      cout << z << endl;
   

   return 0;
}

Output:

The above program will not run and will show a runtime error on the screen because we are trying to divide a number with 0, which is not possible.

Example: code with exception handling

#include <iostream>
using namespace std;

double division(int a, int b) {
   if( b == 0 ) {
      throw "Division by zero condition!";
   }
   return (a/b);
}

int main () {
   int x = 50;
   int y = 0;
   double z = 0;
 
   try {
      z = division(x, y);
      cout << z << endl;
   } catch (const char* msg) {
     cerr << msg << endl;
   }

   return 0;
}

Output:

Division by zero condition!

Using Multiple catch blocks:

In a program, we can use multiple catch blocks to handle different types of exceptions in different ways.

Example:

#include<iostream>

using namespace std;

int main()
{
int a=10, b=0, c;
try
{
	//if a is divided by b(which has a value 0);
	if(b==0)
		throw(c); 
	else
	c=a/b; 		
		
}
catch(char c)     //catch block to handle/catch exception
{
	cout<<"Caught exception : char type ";
}
catch(int i)     //catch block to handle/catch exception
{
	cout<<"Caught exception : int type ";
}
catch(short s)     //catch block to handle/catch exception
{
	cout<<"Caught exception : short type ";
}
cout<<"\n end of execution";
}

Output:

Caught exception : int type 
 end of execution

Standard Exceptions in C++:

C++ comes with a set of standard exceptions defined that we can use in our programs

Exception	Description
std::exception	An exception and parent class of all the standard C++ exceptions.
std::bad_alloc	This can be thrown by new.
std::bad_cast	This can be thrown by dynamic_cast.
std::bad_exception	This is useful to handle unexpected exceptions in a C++ program.
std::bad_typeid	This can be thrown by typeid.
std::logic_error	An exception that theoretically can be detected by reading the code.
std::domain_error	This is an exception thrown when a mathematically invalid domain is used.
std::invalid_argument	This is thrown due to invalid arguments.
std::length_error	This is thrown when a too-big std::string is created.
std::out_of_range	This can be thrown by the ‘at’ method, for example, a std::vector and std::bitset<>::operator[]().
std::runtime_error	An exception that theoretically cannot be detected by reading the code.
std::overflow_error	thrown if a mathematical overflow occurs.
std::range_error	This occurs when you try to store a value that is out of range.
std::underflow_error	This is thrown if a mathematical underflow occurs.

parent-child class hierarchy of exceptions:

Note: also read about Operator Overloading in C++

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