Rethrowing an Exception in C++

An Exception caught can be caught within a try block and handled using one or more Catch Blocks. A few cases exist where the exception is to be caught using a single Catch block and rethrow it, as the Catch block at the top of the Call Stack can handle the corresponding exception. This process can be summarized as Rethrowing an Exception.

Rethrowing an exception while retaining its type and details allows it to propagate further up the call stack. It can be useful when handling different exceptions at multiple program levels or when you need to do additional activities before the exception is resolved.

Example code:

Output:

Caught exception in innerFunction: Exception occurred!
Caught exception in outerFunction: Exception occurred!

Explanation:

In this example, the innerFunction() throws a std::runtime_error. The exception is rethrown using throw; inside the catch block in innerFunction(). It indicates that the catch block of the outerFunction() will again catch the exception. The main() function is handled at the highest level, where the exception can be caught at the end.

Rethrowing exceptions allows you to choose how your program handles them and ensures that they are caught and handled at the appropriate levels.

• An exception's type is preserved when it is rethrown. When an exception is rethrown using the throw; command, it is basically passed up the call stack to be caught and handled by another catch block. The original type of the exception is retained, enabling catch blocks at higher levels to handle particular sorts of exceptions effectively.
• Rethrowing allows for additional processing: You can carry out more operations or log additional information about the exception or change its status before rethrowing it. For instance, you might add debug information, add extra context, or encapsulate the original exception inside another exception to give the higher-level catch block more useful information.
• Catching exceptions by reference: When throwing an exception again, it's crucial to catch it by reference rather than by value (for instance, const std::exception&). When an exception is caught by reference, it is ensured that the exception object will remain valid even after being caught and rethrown numerous times during the exception handling procedure.
• Exceptions rethrown and not caught at any stage of the call stack are known as uncaught exceptions. The exceptions not being caught can be handled by the std::terminate function(), which ceases the code without any stack unwinding or cleaning steps.
• Exception propagation: Throwing exceptions again causes them to advance the call stack until they eventually stop in a catch block, where they can be handled properly. Any function in the call stack can stop the spreading of the exception by catching it and rethrowing it. Exceptions can be dealt with in a manner that is appropriate for the circumstance in which they occur using this strategy.
• Rethrowing with a new exception: You have the option of throwing a new exception in place of the old one when rethrowing an exception. To accomplish this, make a fresh exception object and throw it inside the catch block. Using this method, you can add information to the initial exception before it is caught again higher up the call stack.

• Rethrowing nested exceptions: Exceptions can occasionally be nested, where one exception is raised inside the catch block of another exception. A nested exception that is rethrown will be included as the outer exception's std::nested_exception. If necessary, it enables you to catch and manage the outer and nested exceptions separately.