How to use ifstream - c++

Question

I have a problem with my program which basically is a simple math program. It does some vector multiplication and vector matrix multiplication and it does work fine until i try to read data from a text. I can compile the program but when i try to execute it, I get the fault:" Dataname.exe does not work".
Here's my code. Do not consider the cins and couts
#include<iostream>
#include<cmath>
#include<vector>
#include"header.hpp"
#include<fstream>
using namespace std;
int main()
{
ifstream einlesen ("Zahlen.dat"); //function "einlesen" opens the file "Zahlen.dat".
if (einlesen) // Message if the file has been opend
cout<<"Daten wurden eingelesen"<<endl;
else {
cout<<"Konnte Daten nicht einlesen"<<endl;
return 99;
}
double a;
int n{0};
while ( einlesen >>a>>a>>a>>a>>a>>a>>a) n++;//Loop copys datas on a
einlesen.clear();//stops the loop after the last data is copied.
einlesen.seekg(0, ios_base::beg);//??
vector<double> vecein(n), vecein1(n),Matrixein(n);
for (a = 0;a<n;a++);//copys datas to a vector further calculations
{
einlesen>>vecein.at(a);
einlesen>>vecein1.at(a);
einlesen>>Matrixein.at(a);
}
double Matrix1[9]; //defining my Matrix and the coordinates of my vectors.
double x,y,z,x_1,x_2,x_3;
vector<double> vec(3);
vector<double> vec1(3);
// Old code where I read the data with `cin`:
/*cout<<"Geben Sie die x Koordinaten ein:"<<endl;
cin>>vec[0];
cin>>vec1[0];
cout<<"Geben Sie die y Koordinaten ein:"<<endl;
cin>>vec[1];
cin>>vec1[1];
cout<<"Geben Sie die z Koordinaten ein:"<<endl;
cin>>vec[2];
cin>>vec1[2];
cout<<"Geben Sie eine Matrix ein"<<endl;
cin>>Matrix1[0]>>Matrix1[1]>>Matrix1[2]>>Matrix1[3]>>Matrix1[4]>>Matrix1[5]>>Matrix1[6]>>Matrix1[7]>>Matrix1[8];
cout<<"Vektor1:<"<<vec[0]<<","<<vec[1]<<","<<vec[2]<<">"<<endl;
cout<<"Vektor2:<"<<vec1[0]<<","<<vec1[1]<<","<<vec1[2]<<">"<<endl;
vector<double> Addition(3);
Addition = Vektoraddition(vec,vec1);
cout<<"Addition:"<<"<"<<Addition[0]<<","<<Addition[1]<<","<<Addition[2]<<">"<<endl;
double Skalarprodukt;
Skalarprodukt = Skalarpr(vec,vec1);
cout<<"Skalarprodukt:"<<Skalarprodukt<<endl;
vector<double> kreuzprodukt(3);
kreuzprodukt = Kreuzprodukt (vec,vec1);
cout<<"Kreuzprodukt:"<<"<"<<kreuzprodukt[0]<<","<<kreuzprodukt[1]<<","<<kreuzprodukt[2]<<">"<<endl;
vector<double> MatrixVektor(3);
MatrixVektor = Matrix_vektor (Matrix1, vec);
cout<<"Matrix*Vektor:"<<"<"<<MatrixVektor[0]<<","<<MatrixVektor[1]<<","<<MatrixVektor[2]<<">"<<endl;*/
ofstream ausgabe ("Ausgabe.dat");//write the data on Ausgabe.dat
for (int i = 0; i < a; i++)
{
ausgabe << "(" << vecein[i] << "," << vecein1[i] << "," << Matrixein[i]<<")" << endl;
}
return 0;
}
it's written in German so I don't wonder about the variable names. My problem is that I don't really understand what I'm doing in the while loop. Zahlen.dat is a file similar to 1 2 3 4 5 6 7... and Ausgabe.dat is an empty file. Actually it does write in Ausgabe.dat because it tells me that the content has changed but when I reload the file it's still empty.

Answer 1

I've tried your advice but it still doesn't work. I did not change the way I read my datas because I wanted to see if it works first.
Here is my error message:
terminate called after throwing an instance of 'std::out_of_range'
what(): vector::_M_range_check: __n (which is 10) >= this->size() (which is 10)
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
My code looks like this right now:
int main()
{
ifstream einlesen ("Zahlen.dat");
if (einlesen)
cout<<"Daten wurden eingelesen"<<endl;
else
{
cout<<"Konnte Daten nicht einlesen"<<endl;
return 99;
}
double a;
int n{0};
while ( einlesen >>a>>a>>a>>a>>a>>a>>a) n++;
{
einlesen.clear();
einlesen.seekg(0, ios_base::beg);
vector<double> vecein(n), vecein1(n),Matrixein(n);
int b;// new variable of type int.
for (b = 0;b<n;b++);
{
einlesen>>vecein.at(b);
einlesen>>vecein1.at(b);
einlesen>>Matrixein.at(b);
}
ofstream ausgabe ("Ausgabe.dat");
for (int i = 0; i < b; i++)
{
ausgabe << "(" << vecein[i] << "," << vecein1[i] << "," << Matrixein[i] <<")" << endl;
}
}
return 0;
So I basically only changed the variable of the loop.
Yes the programm did work when I used to get the Data with cin.
I really have no idea why the programm is not working!

Answer 2

There are several things in the first code sample that should be done differently. The program first opens the file, and counts the number of blocks of 7 numbers in the file in variable n. Then the file pointer is reset, three vectors are created with a size of n, and the first n numbers are read into the vector from the file. But: You don't have to know the number of entries in a vector beforehand, so there is no need to read the file twice. Just use vector::push_back to add the numbers.
Second problem: In the loop to read the numbers, a is used as the loop variable, which is a double. The incrementing of a double could result in a one-off error, thus explaining your crash.
I'm also not sure the logic is correct: It seems you expect the file to have several (n) lines of numbers with 7 numbers each, but you then read the first n numbers. Say you have 10 lines, then you read the first line and three numbers of the second line into your vectors, also you might have wanted to read all numbers or maybe the first of each line (or even a 3d structure).
What about the second code sample, where you read from cin? Did that one work? It might help if you explained what you are trying to do, it seems there are vectors in the file, that you want to take the vector product (Kreuzprodukt) of? What is their layout in the file, are they written in lines or columns?
EDIT: The cause for the crash seems to be this line:
for (a = 0;a<n;a++);
{
einlesen>>vecein.at(a);
...
Notice the ; after the loop. This causes the loop to first run without any statement, and the part within brackets runs afterwards, when the loop condition is no longer fulfilled, i.e. a is already equal to n.