 va_copy    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).
 Parameters    dest   -   an instance of the va_list type to initialize 
   src   -   the source va_list that will be used to initialize dest 

  Expanded value (none).
 Example  #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   References 
 C11 standard (ISO/IEC 9899:2011): 
 906.366.7147 The va_copy macro (p: 270) 
 C99 standard (ISO/IEC 9899:1999): 
 906.366.7147 The va_copy macro (p: 250) 
  See also     va_arg   accesses the next variadic function argument  (function macro) 
    va_end   ends traversal of the variadic function arguments  (function macro) 
    va_list   holds the information needed by va_start, va_arg, va_end, and va_copy  (typedef) 
    va_start   enables access to variadic function arguments  (function macro) 
   C++ documentation for va_copy 
  

    
{'path': 'public/docs/c/variadic/va_copy.html', 'source': 'DevDocs.IO'}