C++ 如何将双精度的全精度写入 .dat 文件

Question

我有一个执行辛 ODE 积分的程序 (physics/mathematics)，我想将时间序列导出到 .dat 文件> 但是，写入 dat 文件的数字只有 6 位精度。我写 setprecision(15);在写作之前，但它没有任何改变。我也 post 一部分代码，没有实际的 ODE 求解器：

#include <iostream>
#include <ctime>         
#include <cstdlib>
#include <string>
#include <sstream>             
#include <iomanip>             
#include <cmath>              
#define pi 3.14159265358979
using namespace std;

int main(int argc, char **argv) {
// many stuff here, probably irrelevant,

ostringstream osE, osb, ospx;
    osb<<b; // using this, I can use some numbers into the file's name
    osE<<E;
    ospx<<px0;
filenamex = "Antidot_v4_x(t)_E=" + osE.str() + "_px0=" + ospx.str() + "_b=" + osb.str() + ".dat";
 ofstream file1( filenamex.c_str() );
file1<<t<<"\t"<<x0<<endl;
while(i<=N){
        i++;
        McLachanAtela(x, y, px, py, h);   
// Does the 4-step ODE solver. x are initial values and after the 
// function call x are final values after h time

        setprecision(15);
        file1<<t<<"\t"<<x<<endl; //I use this to write values in file
    }
 return 0;
}

因此，当我打开 file1（它未命名为 file1）时，其中的值是 6 位数字。我怎样才能写出完整的 16 位准确数字？谢谢。为了完整起见，我还 post 调用了 void 函数：

void McLachanAtela (double& previousx, double& previousy, double& previouspx, double& previouspy, double timestep){
    // Atela Coefficients
    double c[4]={0.134496199277431089, -0.224819803079420805, 0.756320000515668291, 0.334003603286321425};
    double d[4]={0.515352837431122936, -0.085782019412973646, 0.411583023616466525, 0.128846158365384185};
    // Symplectic Algorithm (at dimensionless form)
    for(int j=0; j<4; j++){  
                                                        //this is the derivative of the potential :
        previouspx = previouspx - d[j]*timestep*b*pi*sin(pi*previousx)*cos(pi*previousy)*(pow(cos(pi*previousx)*cos(pi*previousy),b-1)); 
        previouspy = previouspy - d[j]*timestep*b*pi*sin(pi*previousy)*cos(pi*previousx)*(pow(cos(pi*previousx)*cos(pi*previousy),b-1));  
        previousx = previousx + c[j]*previouspx*timestep;
        previousy = previousy + c[j]*previouspy*timestep;
        //cout<<" dpx = "<<d[j]*timestep*b*pi*sin(pi*previousx)*cos(pi*previousy)*(pow(cos(pi*previousx)*cos(pi*previousy),b-1))<<endl;

    }
}

Answer 1

您需要将设置的精度注入到流中：

文件 1 << setprecision(15) <<

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