How can I pass an array as parameters to a vararg function?

Question

I have some code that looks like this:

uint8_t activities[8];
uint8_t numActivities = 0;
...
activities[numActivities++] = someValue;
...
activities[numActivities++] = someOtherValue;
...
switch (numActivities)
{
   0 : break;
   1 : LogEvent(1, activities[0]);  break;
   2 : LogEvent(1, activities[0], activities[1]);  break;
   3 : LogEvent(1, activities[0], activities[1], activities[2]);  break;
   // and so on
}

where LogEvent() is a varargs function.

Is there a more elgant way to do this?

[Update] Aplogies to @0x69 et al. I omitted to say that there are many cases where LogEvent() could not take an array as a parameter. Sorry.

refactor _LogEvent_ to accept `LogEvent(1, activities, numActivities)` — Agnius Vasiliauskas, Feb 05 '13 at 11:08
You could just as well pass all of them, if there are few (e.g. 4 max). — Alexey Frunze, Feb 05 '13 at 11:16
Possible duplicate of [Calling a C function with a varargs argument dynamically](http://stackoverflow.com/questions/280940/calling-a-c-function-with-a-varargs-argument-dynamically) — Ciro Santilli OurBigBook.com, Apr 10 '16 at 21:23

score 3 · Accepted Answer · edited May 23 '17 at 11:52

3

There's no standard way to construct or manipulate va_args arguments, or even pass them to another function (Standard way to manipulate variadic arguments?, C Programming: Forward variable argument list). You'd be better off seeing if you can access the internal routines of LogEvent.

edited May 23 '17 at 11:52

Community

1
1

answered Feb 05 '13 at 11:04

ecatmur

152,476
27
293
366

score 2 · Answer 2 · answered Feb 05 '13 at 11:15

pass a pointer to the array of ints and a number of ints instead

#include <stdio.h>

void logevent(int n, int num, int *l) {
    int i;
    for (i=0; i<num; i++) {
        printf("%d %d\n",n,*(l++));
    }
    }

int main() {

    int activities[8];
    activities[0]=2;
    activities[1]=3;
    activities[2]=4;
    int num=3;
    int n=1;
    logevent(n,num, activities);
    printf("=========\n");
    n=2;
    activities[3]=5;
    num=4;
    logevent(n,num, activities);

}

How can I pass an array as parameters to a vararg function?

2 Answers2

Linked