Extract Argument from C Macro -


i have number of definitions consisting of 2 comma-separated expressions, this:

#define pin_alarm  gpioc,14

i want pass second expression of definitions (14 in case above) unary macros following:

#define _pin_mode_output(n)          (1u << ((n) * 2u))

how can extract second number? want macro, call "pick_right", me:

#define pick_right(???)   ???

so can make new macro can take "pin" definitions:

#define pin_mode_output(???) _pin_mode_output(pick_right(???))

and can do:

#define result   pin_mode_output(pin_alarm)

do not use macros this. if must, following work throwing away left part first number remains. use care. no guarantees.

#define pin_alarm  gpioc,14 #define rightpart_only(a,b) b  #define pin_mode_output(a) rightpart_only(a)  #define result   pin_mode_output(pin_alarm)  int main (void) {     printf ("we'll pick ... %d\n", pin_mode_output(pin_alarm));     printf ("or maybe %d\n", result);      return 0; }

if want left part string, can use (with same warnings above), left part gets converted string #:

#define leftpart_only(a,b) #a #define pin_mode_name(a) leftpart_only(a)

there practical reason not entirely without problems. gpioc symbol , such possibly defined elsewhere. fortunately, not problem if undefined, or simple type - after all, first thing macros "throw away left part". jonathan leffler comments

note if gpioc maps macro containing commas, you're compilation errors.


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