In C++, you can create custom exceptions to handle specific errors that are not covered by the standard exceptions provided by the language. To create a custom exception, you need to define a new class that inherits from the standard exception class or one of its derived classes.

Here's an example of a custom exception class that inherits from the standard runtime_error class:

#include <stdexcept>

class MyException : public std::runtime_error {
public:
    MyException() : std::runtime_error("My exception occurred.") {}
};

In this example, the MyException class inherits from the runtime_error class and sets its error message to "My exception occurred." by calling the std::runtime_error constructor with that message.

Once you have defined your custom exception class, you can throw an instance of it in your code to indicate that a specific error has occurred, like this:

throw MyException();

You can catch and handle your custom exception just like any other exception, using a try-catch block:

try {
    // code that may throw an exception
} catch (MyException& e) {
    // handle MyException
}

In this example, the catch block catches the MyException object that was thrown and handles it by executing the code in the block.