Xref: utzoo gnu.g++.help:195 comp.lang.c++:10563
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From: rmartin@clear.com (Bob Martin)
Newsgroups: gnu.g++.help,comp.lang.c++
Subject: Re: initialization of objects within a library
Keywords: c++,library,initialization
Message-ID: <1990Nov28.052118.11028@clear.com>
Date: 28 Nov 90 05:21:18 GMT
References: <3306@danetis.UUCP>
Organization: Clear Communications, Inc.
Lines: 82

I am posting this because your mail bounced...

In article <3306@danetis.UUCP> you write:
>To ensure that global objects of a library is initialized befor its first
>use, I implemented a counter to maintain the number of translation units
>using it (see "the annotated C++ reference manual section 3.4, Ellis &
>Stroustrup).[example below]
>To my confusion, my library objects are constructed (and destructed) twice !
>How can I reduce constructor calls to only ONE for each global object ??
>
>mail, and I will post a summary
>
>engeln@danetis.uucp
>------------------------------- cut here -- nifty_library.h -----------
>..... junk taken out .....
>
>// counter of translation units
>static nifty_counter nifty;

^^^^^^^^^^^^^^^^^^^^^^^^^^^^  This constructs nifty.  The constructor
							  for nifty explicity calls the constructor
							  for foo.  That is the cause of the first
							  aFoo construction by nifty.
>
>#endif nifty_cc
>#endif nifty_h
>------------------------------- cut here -- nifty_library.cc ----------
.....  Junk taken out.
// declare global objects to resolve external references
foo aFoo ("aFoo by library startup");
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
	This causes aFoo to be constructed and so the foo::foo constructor
	is called.  This is the cause of the second construction by
	library startup.

.....  Junk taken out.
>
>// counter implementation
>nifty_counter::nifty_counter ()
>{
>	if (count++ == 0) {
>		// initialize global objects
>		aFoo.foo ("aFoo by nifty_counter");
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
		Ouch!  This makes an explicit call to the contstructor for
		foo.  You should never explicity call a constructor.  It is
		the compiler's job to call constructors.  This will certainly
		cause trouble for you.
>	}
>}
>

You should never ever call a constructor or destructor yourself.  The
compiler will do these things for you...

Let me recommend that you declare the variable "aFoo" as follows:

	foo *aFoo;    <--- as a pointer to a foo.

Now in nifty_counter::nifty_counter() you can create a foo as follows:

	if (count++ == 0)
	{
		aFoo = new foo("aFoo by nifty_counter"); 
			// will call foo::foo for you.
	}

Then in nifty_counter::~nifty_counter() you can destroy the foo
as follows:

	if (--count == 0)
	{
		delete aFoo; // will call foo:~foo for you.
	}

Hope this helps.

-- 
+-Robert C. Martin-----+:RRR:::CCC:M:::::M:| Nobody is responsible for |
| rmartin@clear.com    |:R::R:C::::M:M:M:M:| my words but me.  I want  |
| uunet!clrcom!rmartin |:RRR::C::::M::M::M:| all the credit, and all   |
+----------------------+:R::R::CCC:M:::::M:| the blame.  So there.     |