Re: "PORTING C" > How to assign a value to a define statement?

From:
=?Utf-8?B?Um9iYnk=?= <Robby@discussions.microsoft.com>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 3 Feb 2010 10:57:01 -0800
Message-ID:
<BF2CF98A-F6D1-4A8D-A3D6-0C6792F68B58@microsoft.com>
Thank you fellows for your feedback!

--
Best regards
Roberto

"Igor Tandetnik" wrote:

Robby <Robby@discussions.microsoft.com> wrote:

I am running into a situation where I need some advice on how to do
things. Perhaps I am seeing this the wrong way. In summary, from
main(), I would like to call a defined macro called
"Config_delay_timers", and in that macro I would like to do some
calculations where the result can be assigned to the value of another
#define statement.


This makes no sense. Macros a just text substitutions, performed at compile time. If you want to calculate a value at run time, you need a variable for it.

Please view the following code:
==========================main.h

#ifndef TEST_H
#define TEST_H

// *** SYSTEM OSCILLATION *** //
#define Config_delay_timers(extCrys, fpllidiv, fpllmul, fpllodiv) \
FREQ = (((float)(extCrys/fpllidiv)*(float)(fpllmul/fpllodiv))*1000000)

#define CURR_SYS_OSC FREQ
#define OSC_PERIOD (1.0/CURR_SYS_OSC)

#endif // TEST_H //

=====================================main.c
#include <stdio.h>
#include "test.h"

int main()
{

Config_delay_timers(8, 2, 21, 8);
//SYSTEMConfig(CURR_SYS_OSC, SYS_CFG_ALL);

return 0;
}


Well, since you are hardcoding all the constants anyway, why not something like this:

#define extCrys 8
#define fpllidiv 2
#define fpllmul 21
#define fpllodiv 8
#define FREQ (((float)(extCrys/fpllidiv)*(float)(fpllmul/fpllodiv))*1000000)

If, on the other hand, you expect these values to change from run to run, then you need real functions to calculate them and real variables to store them.

So how is one supposed to carry out a particular
calculation via a define macro and then further assign this result to
other define variables in the program.


One is not supposed to.
--
With best wishes,
    Igor Tandetnik

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