Exception Propagation and Rethrowing
When an exception is thrown in C++, the program looks for a matching catch block starting from the point of the throw and moving up the call stack. If the function where the exception is thrown does not handle it, the exception continues to propagate upward, unwinding the stack, until a suitable handler is found or the program terminates. Deciding where to catch exceptions depends on your program's logic: catch exceptions where you can handle or recover from them, otherwise let them propagate. Sometimes, you may need to catch an exception to perform local actions such as logging, and then rethrow it so that higher-level code can handle the error appropriately.
main.cpp
123456789101112131415161718192021222324#include <iostream> #include <stdexcept> void lowLevelFunction() { throw std::runtime_error("Low-level failure"); } void midLevelFunction() { try { lowLevelFunction(); } catch (const std::exception& e) { std::cerr << "midLevelFunction caught: " << e.what() << std::endl; throw; // Rethrow the same exception to the caller } } int main() { try { midLevelFunction(); } catch (const std::exception& e) { std::cout << "main caught: " << e.what() << std::endl; } return 0; }
Exception Specifications with noexcept
Modern C++ introduces the noexcept keyword to specify whether a function is guaranteed not to throw exceptions. Declaring a function as noexcept tells the compiler and the programmer that the function will not throw, and if it does, the program will call std::terminate. This can enable optimizations and improve code clarity. However, marking a function noexcept when it may actually throw is dangerous, as it can lead to unexpected termination. Use noexcept only when you are certain that no exceptions will escape from the function.
1. Which of the following best describes what happens when an exception is rethrown using throw; inside a catch block?
2. Which statements about the noexcept specifier in C++ are correct? (Select all that apply.)
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When an exception is thrown in C++, the program looks for a matching catch block starting from the point of the throw and moving up the call stack. If the function where the exception is thrown does not handle it, the exception continues to propagate upward, unwinding the stack, until a suitable handler is found or the program terminates. Deciding where to catch exceptions depends on your program's logic: catch exceptions where you can handle or recover from them, otherwise let them propagate. Sometimes, you may need to catch an exception to perform local actions such as logging, and then rethrow it so that higher-level code can handle the error appropriately.
main.cpp
123456789101112131415161718192021222324#include <iostream> #include <stdexcept> void lowLevelFunction() { throw std::runtime_error("Low-level failure"); } void midLevelFunction() { try { lowLevelFunction(); } catch (const std::exception& e) { std::cerr << "midLevelFunction caught: " << e.what() << std::endl; throw; // Rethrow the same exception to the caller } } int main() { try { midLevelFunction(); } catch (const std::exception& e) { std::cout << "main caught: " << e.what() << std::endl; } return 0; }
Exception Specifications with noexcept
Modern C++ introduces the noexcept keyword to specify whether a function is guaranteed not to throw exceptions. Declaring a function as noexcept tells the compiler and the programmer that the function will not throw, and if it does, the program will call std::terminate. This can enable optimizations and improve code clarity. However, marking a function noexcept when it may actually throw is dangerous, as it can lead to unexpected termination. Use noexcept only when you are certain that no exceptions will escape from the function.
1. Which of the following best describes what happens when an exception is rethrown using throw; inside a catch block?
2. Which statements about the noexcept specifier in C++ are correct? (Select all that apply.)
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