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va_copy

Va[医]复制

Defined in header ​​
void va_copy( va_list dest, va_list src ​(since C++11)

大va_copy宏副本src到dest...

va_end应该被召唤dest函数返回或随后重新初始化dest%28va_start或va_copy29%。

参数

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

扩展值

%280%29

例

二次

#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';
}

二次

产出：

二次

0.920258

二次

另见

va_startenables access to variadic function arguments (function macro)
va_argaccesses the next variadic function argument (function macro)
va_endends traversal of the variadic function arguments (function macro)

c VA文件[医]复制

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