va_copy
Min standard notice:
Header: <cstdarg>
The va_copy macro copies src to dest.
# Declarations
void va_copy( std::va_list dest, std::va_list src );
(since C++11)
# Parameters
dest: an instance of the va_list type to initializesrc: the source va_list that will be used to initialize dest
# Example
#include <cmath>
#include <cstdarg>
#include <iostream>
double sample_stddev(int count, ...)
{
double sum = 0;
std::va_list args1;
va_start(args1, count);
std::va_list args2;
va_copy(args2, args1);
for (int i = 0; i < count; ++i)
{
double num = va_arg(args1, double);
sum += num;
}
va_end(args1);
double mean = sum / count;
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 std::sqrt(sum_sq_diff / count);
}
int main()
{
std::cout << sample_stddev(4, 25.0, 27.3, 26.9, 25.7) << '\n';
}