how do you take code out of the main file, and make it a library?

    In assembler, it would be a simple include directive, and nothing
    special need be done to the code that was snipped and exported, but
    this seems not to be the case in C.

    I developed a complete chip init as a series of procedures, and put
    that in a file called init.c, and used: include "init.c" in the main
    file, but the compiler is telling me that within init.c, the port
    names are undefined.

For the equivilent of the Assembler "include" directive (a source-level
"library", so to speak), the #include in C is the correct equivilent.
However, you must make sure that this happens AFTER all the symbols that
are referenced in the inlcude file are already defined.  Your code probably
contains something like:


        #include "init.c"
        #include <cpu_pic16f84.h>

cpu_pic16f84.h contains all the processor specific port names and such, and
since it is included AFTER init.c, init.c doesn't get to use them.
(Assemblers can be a bit more relaxed about this because they're used to
using multiple passes to resolve defintion issue like this.)  The easiest
solution is to make sure your own "library" files come after the "main"
definition files:

        #include <cpu_pic16f84.h>
        #include "init.c"

A BETTER solution is to make sure that all included files are "self
compiling", meaning that they always include all the definitions that
they need, so init.c would look like:

        #include <cpu_pic16f84.h>
        init() {
                /*
                 * initialization
                 */
        }

In order for this to work well, all the ".h" files should be self-compiling
and automatically able to handle multiple inclusions as well.  This is
usually done using a construct like the following:

init.c:
        #idndef INIT_C_INCLUDED         /* If we haven't been included yet */
        #define INIT_C_INCLUDED 1       /*  mark us as included */
        #include <cpu_pic16f84.h>       /* get processor specifics */
        init() { /* etc */ }            /* the code */
          :
        #endif  /* INIT_C_INCLUDED */


cpu_pic16f84.h:
        #ifndef CPU_PIC16F84_INCLUDED   /* included yet ? */
        #define CPU_PIC16F84_INCLUDED 1  /* nope - do it! */
        #define PORTA ....
        #endif /* CPU_PIC16F84_INCLUDED */

Chances are that the .h files supplied with your compiler already do
something like this, and you should probably copy their style for the
sake of consistancy.

Note the DISADVANTAGES of the self-compilable option.  I can imagine an
includable init.c that is carefully processor-independent and relies on a
previous inclusion of the appropriate CPU_whatever file to generate correct
code for the actual target processor.  In that case, you just have to be
careful of your include file ordering (which tends to quickly become a
pain) and document the issue.  The include hierarchy of a large system can
be mind-boggling, and large system utilities (compilers, make utilities,
etc) can contain special case code to optimize the self-compilable include
files so that the preprocessor doesn't actually have to read the file a
dozen times if it ends up included a dozen times...


There are also LINK time libraries commonly used with high level languages
(and sometimes with assemblers, as well.)  In this case, you can compile a
bunch of C files (usually containing not much more than one "externally
visible) function per file) to produce object (.o, usually) files, and use
a library utility of some kind to merge these into a searchable library
file(s) (.a, perhaps)    Something like:
        cc -c init.c -o init.o
        cc -c rs232.c -o rs232.o
        ar -s init.o rs232.o -o picutils.lib

This way you can avoid the (CPU intensive, not that it's likely to be a big
issue for microcontroller sized applications) compile of your (known good)
utilities each time you compile your (new, unproven) program:

        cc seriallcd.c picutils.o

Exact details depend on the compiler, linker, and library utilities in use.
(the above examples are highly "native unix" biased, probably.)

BillW

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