c_macro_tricks

Macro tricks for C/C++.

function substitution

Sometimes you have a function you cannot edit and you cannot edit the caller either. Such as non-user code in a generated file (e.g. STM32CubeMX generated driver files). You can substitute a function without touching changing it. Three ways are used:

• func_sub0.c: original function, then substitute function, then a macro
• func_sub1.c: original function, then a few macros, and a function prototype. You can still explicitly call the original function and even move the substitute function to a different file
• func_sub2.c: original function, static constant that can be overridden locally, and a macro. You can switch which function you call by setting a local variable.

general macros

DEFINE_IS_EMPTY(x) a macro to check if a numerical define is empty. So you can use make a distinction between 0, 1, and empty defines for conditional compilation. Example:

#if defined(USE_FEATURE) && ((USE_FEATURE+0) || DEFINE_IS_EMPTY(USE_FEATURE))

N_ONES(n) is a bitmask of n 1's.

date time macros

• DATE_TO_YEAR(__DATE__) -> int year
• DATE_TO_MONTH(__DATE__) -> int month (1-12, plus 13 for month "???")
• DATE_TO_DAY(__DATE__) -> int day of month (1-31)
• TIME_TO_HOUR(__TIME__) -> int hour (0-23)
• TIME_TO_MIN(__TIME__) -> int min (0-59)
• TIME_TO_SEC(__TIME__) -> int sec (0-59)