Constructor failure

Is there any way you can have a constructor fail so that the class isn't created? i.e.

Code:

---

Socket::Socket(char *addr, int port)
{
    if (connect(addr, port) == FAIL) {
        fail;
    }
}

---

Code:

---

int main()
{
    Socket *sock = new Socket("google.com", 80);
    if (sock == NULL) {
      printf("It didn't work\n");
      return 0;
    }
}

---

You could throw an exception.

Also in your example code new won't return a NULL if it fails. It'll throw an exception.

Another option is to just put the object into a failed state.

Or make an empty constructor and use a Create() member function which returns a bool.

throwing an exception is a easy way

or you can use safe_bool

Code:

---

class A
{
  struct dummy{ void non_null(){} };
  typedef void (dummy::*safe_bool)();
 
  bool init();
public:
  A():is_failed_(false) {  is_failed_ = init();  }
 
  bool failed() const { return is_failed_; }
 
  operator safe_bool() const
  {
      return  (this->failed())? 0 : &dummy::non_null;
  }
private:
  bool is_failed_; 
};

int main()
{
  A a;
  if(a) cout<<"yes"<<endl; else cout<<"no"<<endl;   
}

---

oh cause i picked up the topic...

in case that construction fails how can the memory be cleaned up?
afaik the memory remains - especially when creation of an member fails it cannot free memory of the "parent" object.
i think i read something that the member new and delete functions are used to clean such mess up again...

How to handle a constructor that fails (simple)

How to handle a constructor that fails (long)