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Help with #define substitutiuon

Created Tue, 29 Sep 2015 15:02:28 +0000 by george4657

george4657

Tue, 29 Sep 2015 15:02:28 +0000

I am learning to use defines but this one I can't get to work. I have: #define STEPPERS_DISABLE_PORT D #define STEPPERS_DISABLE_BIT 5 // Max32 pin 39

#define STEPPERS_DISABLE_MASK (1<<STEPPERS_DISABLE_BIT) #define STEPPERS_DISABLE_CLR LATDCLR=STEPPERS_DISABLE_MASK #define STEPPERS_DISABLE_SET LATDSET=STEPPERS_DISABLE_MASK

This works but I would like to have: #define STEPPERS_DISABLE_CLR LAT + STEPPERS_DISABLE_PORT + CLR=STEPPERS_DISABLE_MASK So I only have to change D and 5 to change pin Is this possible:

Thanks George

majenko

Tue, 29 Sep 2015 15:14:26 +0000

Yes, it is possible, but it's not straightforward.

You have to use a multi-later approach to concatenate macros together.

First you need a macro that will concatenate three parameters together:

#define TRIPCAT(A, B, C) A ## B ## C

Then you need one that will parse the parameters as macros and pass them to the TRIPCAT macro (the TRIPCAT macro won't parse them because it's using the token-pasting operator ##):

#define GENLAT(X) TRIPCAT(LAT, X, CLR)

Then you can use that in your final macro:

#define STEPPERS_DISABLE_CLR GENLAT(STEPPERS_DISABLE_PORT)=STEPPERS_DISABLE_MASK

So in total you have:

#define STEPPERS_DISABLE_PORT D
#define STEPPERS_DISABLE_BIT 5 // Max32 pin 39
#define STEPPERS_DISABLE_MASK (1&lt;&lt;STEPPERS_DISABLE_BIT)

#define TRIPCAT(A, B, C) A ## B ## C
#define GENLAT(X) TRIPCAT(LAT, X, CLR)
#define STEPPERS_DISABLE_CLR GENLAT(STEPPERS_DISABLE_PORT)=STEPPERS_DISABLE_MASK

STEPPERS_DISABLE_CLR

That last line is just there to force an invocation for testing - pass that through the preprocessor and you end up with:

$ cpp macro.c 
# 1 "macro.c"
# 1 "&lt;built-in&gt;"
# 1 "&lt;command-line&gt;"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "&lt;command-line&gt;" 2
# 1 "macro.c"
# 9 "macro.c"
LATDCLR=(1&lt;&lt;5)

george4657

Tue, 29 Sep 2015 15:51:22 +0000

Thank you very much. I tried to google for solution but could not find anything close to this. I am converting GRBL to run on a pic32mx and the code is littered with masking functions so having this macro will make it much easier to convert as well as making pin swapping easier.

Thanks George