[avr-gcc-list] Preprocessor question

[Thomas D. Dean]

I have a question about preprocessor syntax.

I want to declare som macros that ease controlling port assignments.

in the include file, I have

#define GLUE(a, b)     (a##b)
#define PORT(x)        (GLUE(PORT, x))
#define PIN(x)         (_BV((x)))
#define DDR(x)         (GLUE(DDR, x))
#define SET_INPUT(x)   ( GLUE(x, _DDR)  |= ~GLUE(x, _PIN ) )
#define SET_OUTPUT(x)  ( GLUE(x, _DDR) |= GLUE(x, _PIN ) )
#define SET_BIT(p,b)   (p |= b)
#define CLR_BIT(p,b)   (p &= ~b)

#define LEFT_MOTOR_DIR_PORT      PORT(C)
#define LEFT_MOTOR_DIR_PIN       PIN(3)
#define LEFT_MOTOR_DIR_DDR       DDR(C)


In the .c file, I have

#include <avr/io.h>
#include <macro.h>
int main() {
  SET_INPUT(LEFT_MOTOR_DIR);
  return 0;
}

# avr-gcc -mmcu=atmega16 -Wall -Wmissing-prototypes -Os -I. 
-I../../../asus-avr-1.0/include -E -o xx macro.c

and, in xx

...
int main() {
  ( ((GLUE(DDR, C))) |= ~(((1 << ((3))))) );
  return 0;
}


The macro is fully expanded on the RHS, but, not the LHS

What did I do wrong?

tomdean