Question

Is there any way (built-in or a code pattern) to ensure that a variadic function is passed the correct number of parameters? (This will be included as part of an API obviously, I can check my own internal code.)

I was considering requiring a UN32 Magic Number to be the last argument passed and check that for validity in the variadic function. Does anyone have any thoughts on that?

Answer 1

You could use the PP_NARG macro to add a count semi-automatically.

int myfunc (int count, ...);
#define MYFUNC(...) myfunc(PP_NARG(__VA_ARGS__), __VA_ARGS__)

MYFUNC(a,b,c,d);
MYFUNC(a,b,c,d,e,f,g);

gcc -E produces:

int myfunc (int count, ...);

myfunc(4, a,b,c,d);
myfunc(7, a,b,c,d,e,f,g);