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+--- Thread: #define a tuple in C (/Thread-define-a-tuple-in-C)
#define a tuple in C - lifemanships4629 - 07-26-2023
I want to be able to define a tuple which represents the arguments needed by other macros.
I think the best way to show what I want is to show an example:
#include <avr/io.h>
#define LED_PORT PORTB
#define LED_DDR DDRB
#define LED_PIN PB7
#define LED LED_PORT, LED_DDR, LED_PIN
#define OUTPUT(port, ddr, pin) ddr |= 1 << pin
void main(void) {
OUTPUT(LED);
}
I want `OUTPUT(LED)` to be then expanded into:
LED_DDR |= 1 << LED_PIN
The problem that I get is to do with the order of expansion, and results in the following error:
> macro "OUTPUT" requires 3 arguments, but only 1 given
This is for use with an AVR project with custom built hardware where I have defined `LED` and other components with a respective `LED_PORT` `LED_DDR` and `LED_PIN`.
I then want to define more macros that can take this LED and use the appropriate arguments to map to the most succinct way possible.
Is this possible with the standard C-preprocessor?
RE: #define a tuple in C - potentates934049 - 07-26-2023
You can add a level of indirection to the macro to achieve this:
#define OUTPUT_I(port, ddr, pin) ddr |= 1 << pin
#define OUTPUT(spec) OUTPUT_I(spec)
During rescanning, `spec` is expanded before `OUTPUT_I`, so the `OUTPUT_I` macro sees three parameters.