为什么我设置了10位的域宽，但结果中PI的值并不是10位？

Question

int main()
{
    double height, row, area, suparea;
    double PI = 3.1415926;
    cout << "请输入底圆半径、高为: ";
    cin >> row >> height;
    area = PI * row * row * height;
    suparea = 2 * PI * row * row + 2 * PI * row * height;
    cout << setw(10) << setiosflags(ios::right) << PI << endl;
    cout << setw(10) << setiosflags(ios::right) << row << endl;
    cout << setw(10) << setiosflags(ios::right) << height << endl;
    cout << setw(10) << setiosflags(ios::right) << suparea << endl;
    cout << setw(10) << setiosflags(ios::right) << area << endl;
    return 0;
}

Answer 1

是10位啊