From: mapson AT mapson DOT com (Mapson)
Newsgroups: comp.os.msdos.djgpp
Subject: Issues making and using libs
Date: Thu, 05 Nov 1998 05:12:11 GMT
Organization: Yale University
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Message-ID: <364132d1.31058536@news.cis.yale.edu>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

I have posted a similar question to a C/C++ newsgroup, but it has
occured to me that one of my questions (executable bloating) may
relate directly to the fact that I am using DJGPP and the "ar" utility
to make libs (".a") files from .o files. 

I need to make two libraries for the project I am doing now- one main
one and one created out of user hardware information. The system
works, but here are some questions I have about it.

First of all, one of the reasons I decided to make libs instead of
just putting the code directly in my source files is that I thought
libs were a way of accessing only what is needed in a given program.
IOW, if I have 25 functions in a lib, and my program only needs 2 of
them, only the object code for two functions is extracted from the
lib. Problem with my theory: the final executables made with the libs
are *considerably* (20%) larger than the same programs with the raw
source code (all 25 functions) built in! Even if my theory was wrong,
I'd have expected them to be close in size... why are my programs so
much larger by linking with the libs?!

Secondly, include files have taken on a new significance with these
libs. I used to keep my global variables in my header files- but in
the case of these libs, they only cause "multiple declaration" errors
later on- even when I uses the standard "#IFDEFINED _THIS_LIB_ ... way
of only including things once. Solution was to pull all variables out
of the include files, put them in the source files for the libs.
Problem: I don't understand why this is true with variables and not
functions- that is, the declared functions certainly don't cause any
problem. There is something I am missing here in my understanding, and
none of my books address this sort of stuff directly. Presently my
theory is that the variables, being global, all are given a default
compiler value ( globals are set to zero by default, right?), and that
is why the multiple declaration errors occur- it is as if each
occurance, rather than a declaration, is also a value assignment.
Wrong?

As usual, lease post here- no e-mail. Thanks.