C++ Throw: Exception Handling Purpose

In C++, the throw keyword is used to throw exceptions. Its purpose is to transfer control to an exception handling program when errors or exceptional circumstances occur in the program, interrupting the normal flow. By using throw, programs can pass exception objects to the exception handling program, allowing for better error and exception handling to increase the reliability and maintainability of the program.

When a program encounters errors or exceptional situations, it can use the “throw” statement to throw an exception, transferring control to the exception handling program. Exception handling programs can catch and handle these exceptions, or continue passing the exceptions to higher-level exception handling programs until they reach a place where the exception can be handled. During the process of handling exceptions, some cleanup operations can be performed, resources can be released, ensuring that the program can still run normally after an exception occurs.

The throw keyword is typically used in conjunction with the try and catch keywords. The try is used to mark a block of code that may throw an exception as an exception handling area, and catch is used to catch and handle exceptions. When an exception occurs, the program will jump to the nearest catch block for handling.

For example, in the code below, an exception of type std::runtime_error is thrown when the divisor is 0.

int divide(int a, int b) {
  if (b == 0) {
    throw std::runtime_error("Divide by zero exception");
  }
  return a / b;
}

int main() {
  try {
    int result = divide(10, 0);
    std::cout << "Result: " << result << std::endl;
  } catch (const std::runtime_error& e) {
    std::cout << "Exception caught: " << e.what() << std::endl;
  }
  return 0;
}

In the above code, the throw statement passes control to the catch block, which catches and handles the exception, then prints out the exception information.