Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!husc6!mailrus!cornell!uw-beaver!uw-june!uw-entropy!dataio!bright
From: bright@Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c++
Subject: Re: Global constructors and C++ I/O streams;  problems and questions.
Message-ID: <1720@dataio.Data-IO.COM>
Date: 24 Oct 88 18:18:08 GMT
Article-I.D.: dataio.1720
References: <5955@columbia.edu> <386@fenix.Atlanta.NCR.COM>
Reply-To: bright@dataio.Data-IO.COM (Walter Bright)
Organization: Data I/O Corporation; Redmond, WA
Lines: 36

In article <386@fenix.Atlanta.NCR.COM> tek@fenix.Atlanta.NCR.COM (Tom Klempay) writes:
>In article <5955@columbia.edu>, beshers@select.columbia.edu (Clifford Beshers) writes:
<< The following program suffers a memory fault before it ever gets
<< to the first line of main().  The problem lies in the constructor
<< of the global instance 'example hello';  the reference to the
<< cout stream occurs before the initialization of that stream.
<< #include <stream.h>
<< struct example {
<< 	example() { cout << "Hello, world\n"; }
<< };
<< example hello; //  Comment out this line and it works, of course.
<< main() { cout << "We never get to the first line...\n"; }
<Just to further muddy the waters, I just tried this with Zortech C++:
<c>foo
<We never get to the first line...
<c>
<It compiles fine (i.e. at least there were no errors or warnings :-), but, as 
<shown above, it ignores the constructor output when "hello" is globally 
<declared.  Something strange going on here since it bombs on you but works 
<(somewhat) for me.

There is nothing strange going on here. cout requires, in order to work,
the static constructor for cout to be called. In C++, the order in which
module constructors are called is not specified when they appear in
different modules. In the example above, cout was not initialized when
example::example() was called, producing random behavior.

Morals:
	1. Don't use stream I/O in constructors.
	2. Don't depend on the order in which module constructors are called.

Definition:
	Module constructor: the function inserted by the C++ compiler
	into each compilation unit (module). This function calls all
	the static constructors for that module, and also does any
	static initialization that cannot be done at compile-time.