How to end C++ code directly from a constructor?

Question

I would like my C++ code to stop running with proper object cleanup if a certain condition is met; in a constructor of a class.

class A {
public:
    int somevar;
    void fun() {
        // something
    }
};

class B {
public:
    B() {
        int possibility;
        // some work
        if (possibility == 1) {
            // I want to end the program here
            kill code;
        }
    }
};

int main() {
    A a;
    B b;
    return 0;
}

How can I terminate my code at that point doing proper cleanup. It's known that, std::exit does not perform any sort of stack unwinding, and no alive object on the stack will call its respective destructor to perform cleanup. So std::exit is not a good idea.

user_2411320 · Answer

You should throw an exception, when the constructor fails, like this:

B() {
  if(somethingBadHappened)
  {
    throw myException();
  }
}

Be sure to catch exceptions in main() and all thread entry functions.

Read more in Throwing exceptions from constructors. Read about Stack unwinding in How can I handle a destructor that fails.

user_7860670 · Answer

It is not possible to perform just from a constructor. If you throw an exception then applications need to set up a proper exception handling code at entry points, because if you just thrown an exception that won't be handled then compiler is allowed to skip stack unwinding and cleanup.

user_245452 · Answer

If you don't want to use use exceptions, you can have an init method in class B that returns a return code:

class B {
public:
    B(/*parameters that will be used by init*/) : ...
    int init(); // actually initialize instance and return non 0 upon failure
}

How to end C++ code directly from a constructor?

3 Answers