Defined in header <cstdarg> | ||
|---|---|---|
void va_copy( std::va_list dest, std::va_list src ); | (since C++11) |
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 <iostream>
#include <cstdarg>
#include <cmath>
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';
}Output:
0.920258
| enables access to variadic function arguments (function macro) |
|
| accesses the next variadic function argument (function macro) |
|
| ends traversal of the variadic function arguments (function macro) |
|
C documentation for va_copy |
|
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/utility/variadic/va_copy