Re: [Libexif-devel] Using libexif

[Benny S. <ich...@pa...>]

Dan,

Thanks for the reply.

The reason I cannot compile libexif into a library as you instructed is that
Rabbit's Dynamic C is not an ANSI C language.  For instance, instead of
#include, it requires #use.  There are other subtle differences that I have
to deal with in order for Dynamic C to accept and compile the libexif files.

I have turned to the Rabbit embedded modules and Dynamic C because I cannot
find an 8-bit microcontroller with 64KB of onboard RAM to allow storage of a
complete Exif header, if necessary.  The Rabbit RCM2300 has 128K of RAM.

I asked about the internals of the libexif/exif-data.h because I am trying
to understand exactly which libexif files (in the list of over 30) that I
have to convert to Dynamic C in order for the library to compile and work
properly.

Surely I am not the first person to use libexif for an embedded application
where memory is limited and where ANSI C may not be fully supported?

Benny   

-----Original Message-----
From: Dan Fandrich [mailto:da...@co...] 
Sent: Sunday, December 14, 2008 9:29 PM
To: lib...@li...
Subject: Re: [Libexif-devel] Using libexif

On Sun, Dec 14, 2008 at 06:24:53PM -0800, Benny Smith wrote:
> I am a new user of libexif and am trying to apply it to an embedded
> application.
> 
> Unfortunately, I am having to tailor the library to the environment
(Rabbit
> Semiconductor?s Dynamic C) that I have chosen.

libexif is quite portable, so you shouldn't have any problem.  If you can
cross compile from a POSIX environment, then it should happen automagically.

> On the main page for libexif (http://libexif.sourceforge.net/internals/
> main.html), it appears that in order to use the library ?libexif?, one
need
> only insert the statement:   #include <libexif/libexif-data.h> .
> 
> Scanning through the code for libexif-data.h, I see lots of #include
statements
> for other libexif header files, but no #include statements for function
files
> such as exif-data.c  or exif-utils.c.  And, the header files that are
#included
> within exif-data.h seem not to contain any invocation of the function
files
> (*.c).
> 
> I expected that #including exif-data.h would, directly and indirectly,
cause
> all files of libexif to be included.
> 
> So, does an application program have to #include the *.c function files
from
> the libexif library separately?
> 
> What am I missing?

It sounds like you're missing the "lib" in "libexif". libexif is designed to
be compiled into a library which is then linked to your application.  The
standard build process creates a libexif.a and/or libexif.so file which
contains all the compiled binaries from the .c files.  When you add the
option "-lexif" to your app's link line (assuming a UNIX-like environment),
the code from the libexif library is added to your application.

You could compile all the .c files yourself, at the same time as your
application, but doing it separately as a library is a cleaner approach.

>>> Dan
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