Why we need Exception handling?

Error handling in C programming is not natively supported, but programmers can access low-level error information through return values. When an error occurs, C functions typically return a value such as -1 or NULL. Programmers can then check these values and take appropriate action. However, using control structures like if-else statements to handle errors can be unreliable. For example, a function that calculates the quotient of a division operation may return 0 when a division-by-zero error occurs. But since 0 is also a valid quotient, it's hard for the calling program to determine if an error has occurred. In these cases, more advanced error handling techniques are necessary.

Exceptions

C++ offers an exception handling mechanism to handle errors or unexpected events that occur during program execution. These exceptions are run-time errors or abnormal conditions that the program encounters. Exception handling in C++ is an advantage over C, as it provides a structured way to handle such situations.

C++ provides the following specialized keywords for this purpose.

• try : represents a block of code that contains success scenario code or it can throw an exception in case of error.
• catch : represents a block of code that is executed when a particular exception is thrown. It contains alternate scenario code.
• throw : Used to throw an exception.

The try and catch keywords come in pairs,If an exception is thrown from a function and there is no catch block to handle it, the program will crash with an error message indicating that the exception was not handled.

Important Points

• Exceptions can be of any type such as int, float, char*, or class objects.
• The catch block must be parameterized with the relevant data type of the exception thrown.
• Multiple catch blocks with different parameters can be used and the appropriate one will execute based on the type of exception thrown.
• A function can either handle exceptions by including local try-catch blocks or throw them to be handled by the caller.

Default Catch-block

A catch block with the ellipsis (...) will catch any type of exception thrown. It can be used as a default handler for any unhandled exceptions. Example: catch(...) Default exception handling.

Object Oriented Approach for Exceptions

In C++, we can use classes to create custom exception types that can be thrown and caught in a more readable and organized way. Instead of throwing raw integers or strings, we can create a class that represents a specific type of exception and throw an object of that class.

System defined exception Classes

In C++, there are several built-in exception classes that can be used to handle specific types of errors. These classes are defined in the <stdexcept> header file.

1. bad_alloc: This exception is thrown by the new operator when memory allocation fails.

2. bad_cast: This exception is thrown by the dynamic_cast operator when a cast is not valid.

3. bad_typeid: This exception is thrown by the typeid operator when it is used with a null pointer.

4. logic_error: This is a base class for other exception classes that indicate errors in program logic. invalid_argument: This exception is thrown when an invalid value is passed to a function.

5. underflow_error: This exception is thrown when the result of an arithmetic operation is smaller than the smallest number that can be stored in a given numeric type.

6. length_error: This exception is thrown when an object's size exceeds its allowed maximum range.
7. out_of_range: This exception is thrown when a value, such as a subscript into an array, exceeds its allowed range of values.
8. runtime_error: This is a base class for other exception classes that indicate execution-time errors.
9. overflow_error: This exception is thrown when the result of an arithmetic operation exceeds the largest number that can be stored in a given numeric type.