Re: MPLAB Pre-processor

On Fri, Jun 26, 2009 at 1:32 AM, Justin Richards
<justin.richards@...>wrote:

> I agree with Olin.  I need help understanding difference between MPLAB and
> the c compiler (in this case c18) and you have helped.


MPLAB is only the IDE, while C18 is the compiler that IDE will invoke when
you do a build.


> I find these processor directives difficult because I cant tell what the
> processor thinks their values are.  I managed to work out how to pass a
> structure by reference because the debugger gives me feedback.


You can invoke the compilation with command line using the MCC18.EXE located
in your MCC18 installation/bin directory, then you can apply -E option to
generate a "<filename>.i" file so you can see what the compiler will see
after the preprocessor.


> Is there a directive that I can use to echo the value of the various
> defines
> or better yet is there documentation that describes these directive.  What
> confuses me even more is that some people put these in a section of their
> code called Macros.


The directives are documented in the C18 user's manual. You can use that -E
option to see your values... However, I would not call it value, as #define
is only defining a macro which is a kind of replacement string. The
preprocessor only blindly replaces the string whatever you put after #define
MAX_TCP_SOCKETS so for example if you have a

myVar = MAX_TCP_SOCKETS;

in your code you will see

myVar = (9ul);

in the .i file... like a search and replace...

But in the .i file you will see NO #if statements whatsoever, those are
already preprocessed by that stage... You need to put a string that the
preprocessor can replace but will not remove or otherwise processes, so you
can even put a plain text without concerning of C language syntax therefore
would not compiled by C18 but at least can be used as a diagnostic on your
preprocessor experiments -- like:

...
...
...
>>> well, the current value of MAX-TCP-SOCKET: MAX_TCP_SOCKETS
...
...
...
(note that I replaces the original underscore to dash otherwise that string
would have been replaced by the preprocessor as well)

Tamas





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