va_copy

va_copy

(C99)

va_end

va_list

[edit]

Defined in header <stdarg.h>

void va_copy( va_list dest, va_list src );

(since C99)

The va_copy macro copies src to dest.

va_end should be called on dest before the function returns or any subsequent re-initialization of dest (via calls to va_start or va_copy).

#include <stdio.h>
#include <stdarg.h>
#include <math.h>
 
double sample_stddev(int count, ...) 
{
 /* Compute the mean with args1. */
 double sum = 0;
 va_list args1;
 va_start(args1, count);
 va_list args2;
 va_copy(args2, args1); /* copy va_list object */
 for (int i = 0; i < count; ++i) {
 double num = va_arg(args1, double);
 sum += num;
 }
 va_end(args1);
 double mean = sum / count;
 
 /* Compute standard deviation with args2 and mean. */
 double sum_sq_diff = 0;
 for (int i = 0; i < count; ++i) {
 double num = va_arg(args2, double);
 sum_sq_diff += (num-mean) * (num-mean);
 }
 va_end(args2);
 return sqrt (sum_sq_diff / count);
}
 
int main(void) 
{
 printf ("%f\n", sample_stddev(4, 25.0, 27.3, 26.9, 25.7));
}