C++ Interview Questions

Exception handling is a crucial aspect of robust C++ programming, and it involves several key concepts: throw, noexcept, and try-catch. Each of these plays a distinct role in managing errors and ensuring that programs can handle unexpected situations gracefully.

The throw keyword is used in C++ to signal the occurrence of an exception. When an exception is thrown, the normal flow of the program is interrupted, and control is transferred to the nearest catch block that can handle the type of exception thrown. This mechanism allows for the propagation of error information up the call stack, providing a way to handle errors at a higher level of the program.

For example:

void mayThrow() {
    throw std::runtime_error("An error occurred");
}

int main() {
    try {
        mayThrow();
    } catch (const std::runtime_error& e) {
        std::cout << "Caught exception: " << e.what() << std::endl;
    }
    return 0;
}

In this code, the mayThrow function throws a std::runtime_error, which is caught by the catch block in main. The catch block handles the exception by printing an error message.

The noexcept specifier, introduced in C++11, is used to indicate whether a function is guaranteed not to throw exceptions. This specifier can be used in two forms: a simple noexcept that indicates the function does not throw, and noexcept(expression) which evaluates to true or false depending on the expression. Declaring a function noexcept provides several benefits, including potential optimizations and clearer code semantics.

For example:

void noThrow() noexcept {
    // This function is guaranteed not to throw exceptions
}

void mayThrow() noexcept(false) {
    throw std::runtime_error("An error occurred");
}

In this code, noThrow is guaranteed not to throw exceptions, while mayThrow explicitly indicates that it may throw exceptions.

The try-catch mechanism is used to handle exceptions. A try block contains code that might throw an exception, and one or more catch blocks follow the try block to handle specific types of exceptions. This structure allows for the separation of normal execution flow from error handling, making the code more robust and easier to maintain.

For example:

int main() {
    try {
        // Code that may throw exceptions
        throw std::runtime_error("An error occurred");
    } catch (const std::runtime_error& e) {
        std::cout << "Caught runtime error: " << e.what() << std::endl;
    } catch (const std::exception& e) {
        std::cout << "Caught exception: " << e.what() << std::endl;
    } catch (...) {
        std::cout << "Caught unknown exception" << std::endl;
    }
    return 0;
}

In this example, the try block contains code that might throw a std::runtime_error. The first catch block handles this specific type of exception, the second catch block handles any other std::exception, and the third catch block handles any other type of exception.

Using throw, noexcept, and try-catch together provides a comprehensive approach to error handling in C++. throw is used to signal errors, noexcept is used to indicate functions that do not throw, and try-catch is used to handle exceptions. By combining these mechanisms, C++ developers can write robust and maintainable code that can gracefully handle unexpected situations and errors.