Exception handling is a crucial aspect of writing robust and reliable code in any programming language, including C++. In certain scenarios, it becomes necessary to catch an exception, perform some additional operations, and then propagate the exception to the calling code. This can be achieved using various techniques in C++. In this blog post, we will explore some techniques for propagating and rethrowing exceptions in C++.

1. Rethrowing an exception using throw;

When an exception is caught, it can be rethrown using the throw; statement. This allows the exception to be passed up the call stack, allowing higher-level code to handle it accordingly. Here’s an example:

try {
    // Some code that may throw an exception
} catch (const SomeException& e) {
    // Additional operations
    
    // Rethrow the exception
    throw;
}

In this example, when the SomeException is caught, additional operations can be performed, and then the exception is rethrown using throw;.

2. Propagating an exception using custom exception types

Another technique for propagating exceptions in C++ is to define and throw custom exception types, which can carry additional information about the error or provide a more specific context. This allows the calling code to catch and handle exceptions based on the custom exception type. Here’s an example:

class CustomException : public std::exception {
public:
    CustomException(const std::string& message) : message_(message) {}
    
    const char* what() const noexcept override {
        return message_.c_str();
    }
    
private:
    std::string message_;
};

void someFunction() {
    try {
        // Some code that may throw an exception
    } catch (const SomeException& e) {
        // Additional operations
        
        // Throw a custom exception
        throw CustomException("Something went wrong");
    }
}

int main() {
    try {
        someFunction();
    } catch (const CustomException& e) {
        // Handle the custom exception
        std::cout << "Caught custom exception: " << e.what() << std::endl;
    }
    return 0;
}

In this example, when an exception of type SomeException is caught in someFunction(), it is further processed, and then a custom exception of type CustomException is thrown. This custom exception can then be caught and handled in the calling code.

By using techniques like rethrowing with throw; and propagating with custom exception types, you can effectively handle and propagate exceptions in C++. This helps in writing more robust and maintainable code. #programming #cplusplus