What is the role of throw and rethrow statements in C++ function exception handling?

The throw statement in exception handling is used to throw exceptions, and the rethrow statement is used to throw the same exception again in the captured exception. The syntax of the throw statement is: throw exception_object; the syntax of the rethrow statement is: rethrow; throw and rethrow statements are only used when errors need to be reported to the caller, and the exception information must be clear and useful.

The throw and rethrow statements in C function exception handling

Exceptions are errors or abnormal situations that occur during runtime. You can use The throw statement throws. The rethrow statement is used to throw the same exception again within the caught exception.

throw statement

throw statement is used to throw an exception object. The syntax is as follows:

throw exception_object;

where exception_object is an exception object, which can be an instance of a standard exception class or a user-defined exception class.

Practical case

Let us consider a function divide(), which calculates the quotient of two numbers. If the denominator is zero, an exception is thrown.

void divide(int a, int b) {
  if (b == 0) {
    throw runtime_error("除数不能为零");
  }
  cout << "商为 " << a / b << endl;
}

rethrow statement

The rethrow statement is used to throw the same exception again in a caught exception. The syntax is as follows:

rethrow;

Practical case

Let us extend the divide() function to capture the runtime_error exception and Use rethrow to throw it again.

void divide(int a, int b) {
  try {
    if (b == 0) {
      throw runtime_error("除数不能为零");
    }
    cout << "商为 " << a / b << endl;
  }
  catch (runtime_error& e) {
    cerr << "错误: " << e.what() << endl;
    rethrow; // 重新抛出异常
  }
}

Usage Tips

• Use throw only when you need to report an error to the caller.
• Rethrow is typically used to handle complex exception handling scenarios involving multiple nested exception handlers.
• Ensure exception information is clear and useful so developers can easily understand and resolve issues.

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