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    <p>You can't define macros in macros, but you can do some other tricks.</p> <p>This is in the "fairly ugly macro" territory. </p> <pre><code>#define MY_CAT(x, y) x ## y #define MY_CAT2(x, y) MY_CAT(x, y) #define LED(x) (MY_CAT2(MY_CAT2(LAT, PORT_ ## x), bits) \ .MY_CAT2(LAT, MY_CAT2(PORT_ ## x, POS_ ## x))) #define PORT_RED E #define POS_RED 2 #define PORT_YELLOW B #define POS_YELLOW 3 #define PORT_GREEN A #define POS_GREEN 4 LED(RED) LED(YELLOW) LED(GREEN) </code></pre> <p>The expansion (check with <code>gcc -E</code>) is:</p> <pre><code>(LATEbits .LATE2) (LATBbits .LATB3) (LATAbits .LATA4) </code></pre> <p>Just because macros are your hammer doesn't mean this is a nail. Try generating the source code with Python or something, much nicer.</p> <pre><code>LEDS = [ ('RED', 'E2'), ('YELLOW', 'B3'), ('GREEN', 'A4'), ] for name, pos in LEDS: print '#define LED_%s (LAT%sbits.LAT%s)' % (name, pos[0], pos) print '#define LED_%s_TRIS (TRIS%sbits.TRIS%s)' % (name, pos[0], pos) </code></pre> <p>The output is:</p> <pre><code>#define LED_RED (LATEbits.LATE2) #define LED_RED_TRIS (TRISEbits.TRISE2) #define LED_YELLOW (LATBbits.LATB3) #define LED_YELLOW_TRIS (TRISBbits.TRISB3) #define LED_GREEN (LATAbits.LATA4) #define LED_GREEN_TRIS (TRISAbits.TRISA4) </code></pre> <p>Then you just go ahead and check both the script and its output into your revision control system.</p> <p><strong>Addendum:</strong> I'm not going to explain how the macro trick works because I don't want to learn the trick well enough to explain it.</p>
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    1. COThanks for the reply. Unfortunately that solution just moves the complexity from the "LED(RED)" line up to the #defines. (and most of the pins aren't LEDs - they're switches, inputs and outputs, etc.) If anything, I think this result is less readable than what I started with. But the example of how to use ## is valuable - thanks for that. I think I'm going to look at an external pre-processor for this.
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