Reading Data From A File - Error

many thnx to MacGyver & Daved...

Problem: i have a data file (*.txt or *.dat), N rows and 3 columns of data. Don't know the N number!
i want to read all the data from the file and see if the data are read properly.


SOLUTION

Code:

---

#include <iostream>
#include <fstream>
#include <vector>
#include <conio.h>
using namespace std;

int main()
{
    vector<double> vList;
    double data;
    fstream file;
    file.open("data.txt",  fstream::in | fstream::out);
       
    while(file>>data)
        vList.push_back(data);

   
    cout<<"Row Tot:"<< vList.size();
    cout<<"\nX"<<"\tY"<<"\tZ"<<endl; 
   
    for(int i=0; i< vList.size()/3.; i++)  // 3. : for 3 columns...
    {
        for(int j=0; j<3; j++)
            cout<< vList[(i*3)+j]<< " ";
        cout<<endl;       
    }
    getch();
}

---

Why are you using fstream::binary?

i was trying everything :(
i took a look at;

Code:

---

http://www.cplusplus.com/reference/iostream/fstream/

---

but couldn't figure it out

http://www.cprogramming.com/tutorial/lesson10.html

thnx for the link but no good

OK, so what is it that you're trying to do? If you don't tell us what your end goal is other than just to store data, we can't guess your intentions, especially since your syntax for declaring arrays was off the mark, and you said you don't know what you're doing with files.

I'm guessing you want us to write some code. Here's a really bad way to read from a file like yours and store the items sequentially in a vector:

Code:

---

#include <iostream>
#include <fstream>
#include <vector>

int main(int argc, char *argv[])
{
        bool bLoop = true;
        unsigned int i,j;
        int iRet = 0;
        double d;
        std::vector<double> vList;
        std::ifstream *input;
       
        if(argc < 2)
        {
                std::cerr << "Usage: " << argv[0] << " <file>" << std::endl;
                return 1;
        }
       
        input = new std::ifstream(argv[1],std::ifstream::in);
        if(input->is_open())
        {
                do
                {
                        *input >> d;
                        if(input->good())
                        {
                                vList.push_back(d);
                        }
                        else bLoop = false;
                }while(bLoop);
                for(i=0;i<vList.size()/3;i++)
                {
                        for(j=0;j<3;j++)
                        {
                                std::cout << vList[(i*3)+j] << " ";
                        }
                        std::cout << std::endl;
                }
        }
        else
        {
                std::cout << "File could not be opened." << std::endl;
                iRet = 2;
        }
       
        delete input;
        return iRet;
}

---

edited my first post...

Well it's no wonder this doesn't work very well:

Code:

---

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

int main()
{
    int i;
    double X[i],Y[i],Z[i]; 
    fstream file;
    file.open("data.txt");
    for(i=0; i<=15; i++)
      file >> X[i] >> Y[i] >> Z[i];

    cout<<"\nX"<<"\tY"<<"\tZ"<<endl;

    for (int i=0; i<=15;i++ ) 
        cout<<X[i]<<"\t"<<Y[i]<<"\t"<<Z[i]<<endl;
    system("pause");
}

---

It's actually a wonder it even compiles. You declare X, Y, and Z to be variable-sized arrays, holding an undefined number of elements, because the variable i has not been initialized.

You should also call file.close() when you're done with the file, and stop using system("pause") if possible, or if not include <cstdlib> . . . see the FAQ.

You could switch your arrays to be pointers and "new" data for them and deal with the memory explicitly by resizing it if you run out, but that gets messy. Another alternative is to use vectors instead of arrays, which is probably preferred.

many thanks MacGyver & dwks, great tips.

i didn't know much about vectors, checked out for a few tips.
your code was very vey helpful MacGyver :)

just a tiny problem left, the last vector is 0.
it doesn't contain a value...

Code:

---

#include <iostream>
#include <fstream>
#include <vector>
#include <conio.h>
using namespace std;

int main()
{
    bool Loop = true;
    vector<double> vList;
    double data;
    fstream file;
    file.open("data.txt");
   
    do
    {
        file >> data;
        if(file.good())
            vList.push_back(data);
        else
            Loop = false;
    }
    while(Loop);
   
    cout<<"\nX"<<"\tY"<<"\tZ"<<endl; 
    for(int i=0; i<=vList.size()/3; i++)
    {
                for(int j=0; j<3; j++)
                      cout<< vList[(i*3)+j]<< " ";
                cout<<endl;       
    }
    getch();
}

---

So changing to < fixed that problem?

BTW,

Code:

---

    do
    {
        file >> data;
        if(file.good())
            vList.push_back(data);
        else
            Loop = false;
    }
    while(Loop);

---

could be changed to:

Code:

---

    while (file >> data)
    {
        vList.push_back(data);
    }

---

maybe a little silly, i had to edit my txt file.
i had to drop the cursor to a empty line and save it. (before it was at the end of the data)

Code:

---

before
1 2 4
2 4 3|

---

Code:

---

after
1 2 4
2 4 3
|

---

Code:

---

while (file >> data)
    {
        vList.push_back(data);
    }

---

works great thnx

I think making the change to while (file >> data) would allow it to work with either version of the text file. Calling file.good() returns false if there was a failure or if eof was reached. In your original input file, the 3 is the last character, so on the last read 3 is read into data and the eofbit is set. The call to good() returns false and so the 3 is never pushed on to the vector. With my code, the operator>> returns !fail(), so if the read succeeds it will allow the object to be pushed back, even if the eof is reached at the same time.

definetly works :)
it's intresting about good() returning false at the last data.

thanks daved and MacGyver for all of your help. finally a worknig nice script...