How to Throw Out of Range Exception in C++

1. Throw Out of Range Exception in C++
2. Error While Throwing Out of Range Exception in C++

In C++, we can handle exceptions using try-catch blocks. We can also throw an exception explicitly using the throw statement.

This article discusses how to throw an out-of-range exception in C++.

Throw Out of Range Exception in C++

To throw an out-of-range exception in C++, you can create an exception object. For this, you can use the out_of_range() constructor.

The out_of_range() constructor is defined in the standard C++ library. It takes a string object as its input argument and returns an out-of-range exception.

You can throw the exception using the throw statement, as shown in the following example.

#include <iostream>

int main() {
  int number = 100;
  if (number > 50) {
    throw std::out_of_range("I am an exception.");
  }
  return 0;
}

Output:

terminate called after throwing an instance of 'std::out_of_range'
  what():  I am an exception.
Aborted

Here, we have first created a variable named number. Then, we have checked if the value in the number is greater than 50.

If yes, we have thrown an out-of-range exception defined in the standard C++ library.

You can also handle the out-of-range exception using try-catch blocks. We will throw the exception in the try block.

We will catch the out-of-range exception and print that we have handled the exception in the catch block. You can observe this in the following example.

#include <iostream>

int main() {
  int number = 100;
  try {
    if (number > 50) {
      throw std::out_of_range("I am an exception.");
    }
  } catch (std::out_of_range) {
    std::cout << "I am here. Exception caught and handled.";
  }
  return 0;
}

Output:

I am here. Exception caught and handled.

The above output shows that the program has terminated normally after handling the out-of-range exception. On the other hand, the previous program was aborted because we did not handle the exception.

Error While Throwing Out of Range Exception in C++

It is sometimes possible to write a program to throw an out-of-range exception in C++, as shown below.

#include <iostream>

int main() {
  int number = 100;
  try {
    if (number > 50) {
      throw std::out_of_range;
    }
  } catch (std::out_of_range) {
    std::cout << "I am here. Exception caught and handled.";
  }
  return 0;
}

When we run the above code, the program will run into an error with the following execution trace.

/tmp/EG06BKsTcd.cpp: In function 'int main()':
/tmp/EG06BKsTcd.cpp:8:36: error: expected primary-expression before ';' token
    8 |             throw std::out_of_range;
      |                                    ^

The error occurs because we have thrown std::out_of_range instead of an out-of-range exception object. The std::out_of_range constructor is a type definition used to create an out-of-range exception.

Hence, you cannot throw it using a throw statement. To throw an out of range exception in C++, you must create an out of range exception by passing a string as an input argument to the std::out_of_range() constructor; only then will you be able to throw the out of range exception successfully in C++.