Usage of varargs in C

Question

Here is the example of varargs.

I'm a little puzzled.

va_list ap;
va_arg (ap + (n-1), int); // **INCORRECT USAGE**

Is it correct? If not, how to get the n^th argument?

It says ap will increase to the next argument, but if I use va_arg(ap + (n-1), int), n>=2, will ap increase?

Sometimes, we declared Cnt abbreviated from Count or Counter.

What's ap abbreviated from?

I know it's va_list type, but what is va_list? struct? int? or something else?

Thanks.

`ap` is for additional parameters – StoryTeller - Unslander Monica Dec 07 '13 at 10:48 — StoryTeller - Unslander Monica, Dec 07 '13 at 10:48
`ap` might also be for *argument pointer* – Jens Dec 07 '13 at 10:55 — Jens, Dec 07 '13 at 10:55
@self. Yes. That was a typo. sorry. – Kevin Dong Dec 07 '13 at 12:40 — Kevin Dong, Dec 07 '13 at 12:40

this · Accepted Answer · 2013-12-07T12:43:53.457

6

If you want the n-th argument you will have to call va_arg() with correct type n-1 times.

Your examples 1 and 2 are wrong. ap will be changed by va_arg() automatically.

Type of va_list is implementation defined, but is usually a char*.

edited Dec 07 '13 at 12:43

answered Dec 07 '13 at 10:47

this

1 Answers1