va_copy
Defined in header <cstdarg>
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void va_copy( va_list dest, 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).
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
Run this code
#include <iostream> #include <cstdarg> #include <cmath> double sample_stddev(int count, ...) { double sum = 0; va_list args1; va_start(args1, count); 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
See also
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) |