How to Throw an Exception in C++?

In C++, exception handling is a mechanism that allows us to handle runtime errors and exceptions are objects that represent an error that occurs during the execution of a program. In this article, we will learn how to throw an exception in C++.

Throw a C++ Exception

Throwing an exception means sending the exception to the catch block after it has occurred in the program. To throw an exception in C++, we can use the throw keyword followed by an instance of the exception. When a program encounters a throw statement, then it immediately terminates the current function and starts finding a matching catch block to handle the thrown exception. Generally throw is used inside a try block or a function that is called within a try block. 

Syntax to Throw an Exception in C++

throw exception_object

Here, exception_object is typically an instance of an exception class that can be a built-in type (like int or const char*), but more commonly, we use a class derived from std::exception.

C++ Program to Throw an Exception

The following program illustrates how we can throw an exception in case of divide by zero runtime error in C++.

C++

// C++ Program to illustrate how to throw an exception
#include <iostream>
#include <stdexcept>
using namespace std;

// Function to perform division
void divide(int x, int y)
{
    // Check if the denominator is zero
    if (y == 0) {
        // If denominator is zero, throw an exception of
        // type runtime_error
        throw runtime_error("Division by zero error");
    }
    // If denominator is not zero, perform division and
    // print Result
    cout << "Result: " << x / y << endl;
}

int main()
{
    try {
        divide(10, 0);
    }
    catch (const exception& e) {
        // Catch any exception thrown during the execution
        // of divide function
        cerr << "Exception caught: " << e.what() << endl;
    }
    return 0;
}

Output

Exception caught: Division by zero error

Time Complexity: O(1)
Auxiliary Space: O(1)