All standard exception classes derive ultimately from the class exception, defined in the header . The two main derived classes are logic_error and runtime_error, which are found in (which itself includes ). The class logic_error represents errors in programming logic, such as passing an invalid argument. Runtime errors are those that occur as the result of unforeseen forces such as hardware failure or memory exhaustion. Both runtime_error and logic_error provide a constructor that takes a std::string argument so that you can store a message in the exception object and extract it later with exception::what( ) , as the following program illustrates^.

//: C01:StdExcept.cpp

// Derives an exception class from std::runtime_error

#include

#include

using namespace std;

class MyError : public runtime_error {

public:

  MyError(const string& msg = "") : runtime_error(msg) {}

};

int main() {

  try {

    throw MyError("my message");

  }

  catch (MyError& x) {

    cout << x.what() << endl;

  }

} ///:~

Although the runtime_error constructor passes the message up to its std::exception subobject to hold, std::exception does not provide a constructor that takes a std::string argument. Therefore, you usually want to derive your exception classes from either runtime_error or logic_error (or one of their derivatives), and not from std::exception^.

The following tables describe the standard exception classes.

The iostream exception class ios::failure is also derived from exception, but it has no further subclasses^.

You can use the classes in both of the following tables as they are, or you can use them as base classes from which to derive your own more specific types of exceptions^.

Exception specifications