C preprocessor: concatenation of another define

Question

I'm coding for a ARM with GCC and need to concatenate (##) a name with the a definition, like this:

#define LCD_E_PORT GPIOC 
...
#define RCC_PORT(x) (RCC_APB2Periph_ ## (x)) // ???
...

so that afterRCC_PORT(LCD_E_PORT) I would get RCC_APB2Periph_GPIOC. It is important to say, that the LCD_E_PORT and the RCC_APB2Periph_GPIOC are NOT strings but some low-level system defined pointers (accessing them processor's memory map).

The point of all this is to have one macro, which handles multiple port definitions.

Is there a solution for this?

Removed parantheses
With parentheses

I'm using arm-none-eabi-gcc.

What happens if you try `#define RCC_PORT(x) RCC_APB2Periph_##x` ? — Paul R, Feb 26 '15 at 11:03
For example: `RCC_PORT(LCD_E_PORT)` will result in `RCC_APB2Periph_LCD_E_PORT` so it is wrong. I've also tried double definition, I mean: `#define RCC_PORT1(x) RCC_PORT(x)` but after `RCC_PORT1(LCD_E_PORT)` I get an error that `RCC_APB2_Periph_ and "(" don't give a valid token` because, like I said, the GPIOx is a `(u32 *) ptr`. It is that or it doesn't expand macros, or it expands macros to the final definition... All what I need is the definition in the middle. — Grzegorz Grzeda, Feb 26 '15 at 11:35

score 4 · Answer 1 · edited May 23 '17 at 10:09

The kind of thing you need required more indirection through the pre-processor:

This (defines.c) :

#define TOKENPASTE( x, y ) x ## y
#define TOKENPASTE2( x, y ) TOKENPASTE( x, y )

#define LCD_E_PORT GPIOC
#define RCC_PORT(x)  TOKENPASTE2( RCC_APB2Periph_, x )

#define STRING(x) #x

int main( int argc, char* argv[] )
{
    RCC_PORT(LCD_E_PORT);
}

results in the expected output through gcc -E defines.c we get:

# 1 "defines.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "defines.c"
# 10 "defines.c"
int main( int argc, char* argv[] )
{
    RCC_APB2Periph_GPIOC;
}

See this SO question for more information.

C preprocessor: concatenation of another define

1 Answers1

Linked