Date: Wed, 25 Aug 1999 12:51:22 +0200
From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Message-Id: <199908251051.MAA31093@acp3bf.physik.rwth-aachen.de>
To: anne DOT hawson AT virgin DOT net (Anne Hawson)
Cc: djgpp AT delorie DOT com
Subject: Re: I can't compile with the -O2 switch.
Newsgroups: comp.os.msdos.djgpp
Organization: RWTH Aachen, III. physikalisches Institut B
X-Newsreader: TIN [version 1.2 PL2]
Reply-To: djgpp AT delorie DOT com

In article <7purvn$j7h$1 AT nclient11-gui DOT server DOT virgin DOT net> you wrote:
> I wanted to compile C++ code into an executable with optimisations.

> In this case, it is a tiny program called "keypress.cpp"
> (pasted at the end of this message).
> It compiles fine with -

> >  gxx -o keypress.exe keypress.cpp
> but complains with -

> >  gxx -O2 keypress.exe keypress.cpp

That's because there's a major error in that command line. It ought
to have been

	gxx -O2 -o keypress.exe keypress.cpp

The '-O2' is one option, and '-o keypress.exe' is another one. These
two have almost nothing to do with each other:

'-O2' means: optimize the code

'-o keypress.exe' means: call the resulting program 'keypress.exe', instead
                         of the default 'a.exe' (and 'a.out').

Your command line is interpreted as:

	compile keypress.c (to keypress.o)
then    link keypress.exe and keypress.o, forming the new program 'a.exe'

Obviously, that can't work, as keypress.exe is not usable as a part of
a program, it's a full program on its own.

--
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.