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).
| dest | - | an instance of the va_list type to initialize |
| src | - | the source va_list that will be used to initialize dest |
(none).
#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));
}Possible output:
0.920258
| accesses the next variadic function argument (function macro) |
|
| ends traversal of the variadic function arguments (function macro) |
|
| holds the information needed by va_start, va_arg, va_end, and va_copy (typedef) |
|
| enables access to variadic function arguments (function macro) |
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