Message-ID: <37916761.BFEE55@vetec.com>
Date: Sun, 18 Jul 1999 00:34:25 -0500
From: Andy Goth <andygoth AT vetec DOT com>
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To: djgpp AT delorie DOT com
Subject: Re: Marker
References: <378E8DD5 DOT 68B571A AT vetec DOT com> <7mnnns$39l$1 AT news DOT luth DOT se> <37914616 DOT 11FEAA6C AT vetec DOT com> <37915EED DOT 5D68DAC AT cartsys DOT com>
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Reply-To: djgpp AT delorie DOT com

> > > : Is there any way of inserting a marker into C code that is compiled but
> > > : not run?  It would be really helpful if I could put comments (of a sort)
> > > : right into the binary.
> > > :
> > > : I imagine that maybe I could do it with inline assembly that jumps over
> > > : a text string, but would the optimizer throw that out?
> > >
> > > Hmm. Will the compiler remove 'const char s[] = "My string\n";'?
> > >
> > > If it does try 'struct { char s[], void *p } my_var = { "My string\n",
> > > &my_var };' wihch I haven't tested but should work. The trick is to
> > > make sure you reference the string somewhere in the code.
> >
> > What does the void* p part do (besides add four extra unused bytes)?
> 
> The structure needs to be referenced.  If it has a pointer in it, it can
> reference itself.  Neat trick, that.

Yes, it's neat.  New question!!  I'm just checking here.  The following
compiles in DJGPP, but I am unsure whether or not it is standard.  Here
goes...

Classes I use in this example: ReqDrawMsg, Message, Box, Point, and
Screenport

ReqDrawMsg's constructor takes (const Box&).  ReqDrawMsg is derived from
Message.  Box's constructor takes (const Point&, const Point&).  Point's
constructor takes (int, int).  Screenport has an operator<< that takes
(const Message&).

// #includes

int main()
{
   Screenport theScreen;
   theScreen << ReqDrawMsg(Box(Point(5, 5), Point(20, 20)));

   return 0;
}

The whole point of this is to avoid the clumsy alternative:

int main()
{
   Screenport theScreen;

   Point ul(5, 5);
   Point lr(20, 20);
   Box box(ul, lr);
   ReqDrawMsg draw(box);

   theScreen << draw;

   return 0;
}

Am I free to use the first version?  Does it compile *correctly*?  I
can't test that yet since no functions have implementations.  Will it
compile correctly on other platforms and other (working) compilers?  Are
there any gotchas I should be aware of?

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