Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!mstan!jordan
From: jordan@Morgan.COM (Jordan Hayes)
Newsgroups: comp.lang.c++
Subject: "Failed" constructors
Message-ID: <291@zooks.Morgan.COM>
Date: 29 Jun 89 18:24:36 GMT
Reply-To: jordan@Morgan.COM (Jordan Hayes)
Distribution: usa
Organization: Morgan Stanley and Co., NY, NY
Lines: 28

Is there any convention for how to return from a constructor that has
"failed" ... for instance, consider a fascist parent who won't let you
look at TV during school hours ... the constructor could check the time
of day, and if it's not during school hours, allocate you a TV object,
and your code continues.  What to do if it's 1pm?  Can a constructor
"return NULL" so you could say

	TV	*my_tv;

	if ((my_tv = new TV("HBO")) == NULL)
		go_read_a_book();

I took a quick look through a bunch of C++ code I have lying around,
but couldn't find any exmples of constructors that "return" something.
Further, if a constructor decided to "abort" a construction, could the
destructor get called?

Or, am I doomed to have to write

	my_tv = new TV("ESPN");
	if (my_tv->Valid() == FALSE) {
		delete my_tv;
		go_read_a_book();
	}

Thanks.

/jordan