如何保留小数

头文件：<iomanip>

#include<iostream>#include<iomanip>using namespace std;int main(){    double a=3.141111;double b = 3.149999;cout << fixed << setprecision(2) << a << " "<<b<<endl;//#1cout << setiosflags(ios::fixed) << setprecision(2) << a << " " << b << endl;//#2cout.precision(2);//#3cout <<  a<<" " << b << endl;//三种方式输出的都是3.14 3.15//采取四舍五入原则return 0;}