Thread: read file without ifstream

I have an example code for reading a file and working with the values in c++ but I don't understand how it works:

Code:

#include <iostream>
#include<fstream>
using namespace std;


class v3d{


  double x,y,z;
public:
   v3d(double a=0,double b=0,double c=0){x=a; y=b; z=c;}
   void  operator+=(v3d a);
   friend ostream& operator<<(ostream& out, const v3d &s);
   friend v3d  operator*(double a, v3d b);
};


v3d  operator*(double a, v3d b){
     return v3d(a*b.x,a*b.y,a*b.z);
     }


void v3d::operator+=(v3d a){
 x+=a.x;y+=a.y;z+=a.z;
}


ostream& operator<<(ostream& out, const v3d &s)
{
 out << s.x << "   " << s.y << "   " << s.z;
 return out;
}




int main(void){
  int i;
  v3d s(0,0), v(2,2), F(0,-10);
  double dt=1e-2,m=1.;
  for (i=0;i<40;i++){
     v+=1./m*dt*F;
     s+=dt*v; 
     cout << i*dt << "   " << s << "  " << v << endl; 
     }
}

This programm reads a file called "move.dat". I don't understand how this works. There is not even the name of the file and still it works. Can somebody pleas explain me where and how the reading is done?

Seems you don't have the complete code. There is no fstream or ifstream declared for reading from a file, neither is there a reading from the console.
It just produces the following output from hardcoded input.

Code:

0   0.02   0.019   0  2   1.9   0
0.01   0.04   0.037   0  2   1.8   0
0.02   0.06   0.054   0  2   1.7   0
0.03   0.08   0.07   0  2   1.6   0
0.04   0.1   0.085   0  2   1.5   0
0.05   0.12   0.099   0  2   1.4   0
0.06   0.14   0.112   0  2   1.3   0
0.07   0.16   0.124   0  2   1.2   0
0.08   0.18   0.135   0  2   1.1   0
0.09   0.2   0.145   0  2   1   0
0.1   0.22   0.154   0  2   0.9   0
0.11   0.24   0.162   0  2   0.8   0
0.12   0.26   0.169   0  2   0.7   0
0.13   0.28   0.175   0  2   0.6   0
0.14   0.3   0.18   0  2   0.5   0
0.15   0.32   0.184   0  2   0.4   0
0.16   0.34   0.187   0  2   0.3   0
0.17   0.36   0.189   0  2   0.2   0
0.18   0.38   0.19   0  2   0.1   0
0.19   0.4   0.19   0  2   -6.38378e-16   0
0.2   0.42   0.189   0  2   -0.1   0
0.21   0.44   0.187   0  2   -0.2   0
0.22   0.46   0.184   0  2   -0.3   0
0.23   0.48   0.18   0  2   -0.4   0
0.24   0.5   0.175   0  2   -0.5   0
0.25   0.52   0.169   0  2   -0.6   0
0.26   0.54   0.162   0  2   -0.7   0
0.27   0.56   0.154   0  2   -0.8   0
0.28   0.58   0.145   0  2   -0.9   0
0.29   0.6   0.135   0  2   -1   0
0.3   0.62   0.124   0  2   -1.1   0
0.31   0.64   0.112   0  2   -1.2   0
0.32   0.66   0.099   0  2   -1.3   0
0.33   0.68   0.085   0  2   -1.4   0
0.34   0.7   0.07   0  2   -1.5   0
0.35   0.72   0.054   0  2   -1.6   0
0.36   0.74   0.037   0  2   -1.7   0
0.37   0.76   0.019   0  2   -1.8   0
0.38   0.78   -2.15106e-16   0  2   -1.9   0
0.39   0.8   -0.02   0  2   -2   0

You probably got mixed up with another executable. This code does not do file I/O.

p.s. You should really start to work in your formatting. The first week learning C++ that's excusable, but by now your code should be consistently formatted (even if you took it from somewhere else).

I was wondering that there is no ifstream too, but the strange thing is, that this are the numbers from my file. So I have no idea why you are getting this values without having the file.

Originally Posted by Gamma_123

So I have no idea why you are getting this values without having the file.

The numbers are calculated and print in this loop:

Code:

for (i=0;i<40;i++)
{  
  v+=1./m*dt*F;
  s+=dt*v; 
  cout << i*dt << "   " << s << "  " << v << endl; 
}

I just saw it. Thanks for your help anyway. I should check my sources better.