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va_arg

Va[医]阿格

Defined in header ​​
T va_arg( va_list ap, T ​​

大va_arg宏展开为类型表达式。T的下一个参数。va_listap...

打电话前va_arg，，，ap必须通过调用va_start或va_copy，没有任何介入的电话va_end.每次调用va_arg宏修改ap指向下一个变量参数。

如果va_arg中没有更多的参数时调用ap中的下一个参数的类型ap%28升级后%29不兼容T，行为未定义，除非：

  • 一种类型是有符号整数类型，另一种类型是对应的无符号整数类型，并且值在这两种类型中都是可表示的；或

  • 一种类型是指向void另一个是指向字符类型%28的指针char，，，signed char，或unsigned char29%。

参数

ap-an instance of the va_list type
T-the type of the next parameter in ap

扩展值

中的下一个变量参数ap...

例

二次

#include <iostream>
#include <cstdarg>
#include <cmath>
 
double stddev(int count, ...) 
{
    double sum = 0;
    double sum_sq = 0;
    va_list args;
    va_start(args, count
    for (int i = 0; i < count; ++i) {
        double num = va_arg(args, double
        sum += num;
        sum_sq += num*num;
    }
    va_end(args
    return std::sqrt(sum_sq/count - (sum/count)*(sum/count)
}
 
int main() 
{
    std::cout << 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_copy (C++11)makes a copy of the variadic function arguments (function macro)
va_endends traversal of the variadic function arguments (function macro)

c VA文件[医]阿格

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