Reading files

How can I read this line of numbers, assigning each to a different variable.

1 3 4 7 2 3 5 1 2 4 1 1

I need to account for the possability of some of the ints being double or tripple digit.

Im sorry, but u sound liek a newbie. Maybe you should get a book, or read some tutorials, or I could teach you if u want. Its not hard.

SPH

well, ive been codeing about a year and a half, but I am self taught, so some things ive just never had to deal with. One of those is file I/O, so when it comes to that I am a newbie.

I thought my question was rather simple and straitforward?

file io is much as any other io, if you do not understand hwo to do thisfrom a string, you will most likely not understand how it is being done from a file, for not understanding your own code is the worst thing of all. so I suggest you practise doing this with strings (by makking a class with a streampos to read along) and then I will give you some file io code using fstreams.

SPH

I found this code some time back, I understand it, but it only demonstrates reading one value at a time.

#include <fstream.h>
#include <iostream.h>
#include <stdlib.h>
int main()
{
int array[10] = {1,7,3,6,2,6,6,2,8,1};

//creating output stream object to be used when saving
ofstream output;

//opening file to write to
output.open("file.txt");

int i;

//looping through all elements of the array and writing everything to the file
for (i = 0; i < 10; i++)
{
output << array[i] << endl;
}

//closing the file
output.close();

//declare array to hold data
int array2[10];

//reset i to zero;
i = 0;

//declare ifstream, associate with file, and open file
ifstream fin("file.txt");

//check if opening file not successful
if(!fin)
{
cout << "couldn't open file for reading." << endl;
}

//read in one int at a time into array2
while(fin)
{
fin >> array2[i++];
}

//display array2 to show that read in was successful
for(i = 0; i < 10; i++)
{
cout << array2[i] << endl;
}

return 0;
}

wow... that looks lust like the example that i always use...

well, here's how i do it.. it's probably the same as the above, but jsut incase something was missed.

Code:

---


#include <iostream.h>
#include <stdlib.h>
#include <fstream.h>

int main()
{
 //creating input stream to read from file into program
 ifstream input;
 
 //creating output stream to write to a file from the program

 //opening file to read into the program using the previously created input stream.
 input.open("test.txt");
 
 //reading in the variables from the file and saving them into an array within the program
 cout << "how many different numbers are in the file?" << endl;
 int num_lines;
 cin >> num_lines;
 
 int array[num_lines];

 for (int i = 0; i < num_lines; i++)
 {
  cin >> array[i];
 }

 //whether to print the array to another file or to the screen
 char choice;
 do
 {
  cout << "print to [f]ile or print to [s]creen?" << endl;
  cin >> choice;
 }while (choice != 'f' && choice != 's');
 
 //printing the array to a file
 if (choice == 'f')
 {
  //creates an output stream to write to a file with
  ofstream output;
 
  //opens a file to write to  using the output stream
  output.open("ofile.txt");

  //cycles through the array and prints it to file
  for (i = 0; i < num_lines; i++)
  {
    output << array[i];
  }
  }
 
 //printing the array to the screen
 if (choice == 's')
 {
  //cycles through the array and print it to the screen
  for (i = 0; i < num_lines; i++)
  {
  cout << array[i];
  }
 }
}

---

you can use such functions as atof() and read in the numbers as strings and convert them to the appropriate format...

You cant do

int array[num_lines];

can you?

I though you had to declare all array sizes at compile time, so the program will know how much memory to allocate, here you are declareing an array, and useing a variable to set the size. I tried something along that line a while back, and it never would work.

Quote:

---

I though you had to declare all array sizes at compile time

---

You do, but some compilers (Dev C++ is one) will let you do what Aran has, but as it's highly non-standard, it's not very good practice.

You could either manage your arrays dinamically using new and delete ,use something like the c++ vector template or use your own data structure.

Thanks for backing me up zen, but that still dosent answer my question.

how can i read this line of numbers from a file

1 3 2 4 5 6 3

and then this line useing the same code

23 1 4 5 32 2 5

If i just read in one charcter at a time, double digits will throw me off.

Whats the answer?

Code:

---

#incude <fstream.h>

void main()
{
    int n1,n2,n3,n4,n5;
    ifstream file("blah.txt");
    file>>n1>>n2>>n3>>n4>>n5;
    file.close();
}

---

I just hink you need to think for yourself a little.

SPH:rolleyes:

Code:

---

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

int main()
{
    int num[10];
        int i = 0;
    ifstream file("text.txt");
    while(file>>num[i++]);
        file.close();
        --i;
        while(i)
        {
                cout << num[--i] << endl;

        }
        return 0;
}

---

I'm not a C++er so this could be improved but I would think that you would want to use an array for this or else a vector.

Maybe I'll try to come up with the vector code.

Code:

---

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

int main()
{
        vector<int> v_numbers;
        int x;
        ifstream file("text.txt");
        while(file >> x) v_numbers.push_back(x);
        file.close();

        for(vector<int>::size_type size = 0; size < v_numbers.size(); ++size)
        {
                cout << v_numbers[size] << endl;
        }
        return 0;
}

---

This is more the C++ers way!

I'm a C++er and i still don't know crap about vectors.... oooooo
i just remembered the encryption system that i was going to program today.... *opens up dev-cpp and starts coding*

Read up on the different istream member functions/operators like >> and get() and getline(). They are used in both cout and any user defined streams like those used to read in files, etc. In a nutshell I use the >> operator if I want to read in a discrete variable delimited from other variables by whitespace and getline() when I want to read in an entire string that may (or may not) have embedded whitespace, parsing the input string when necessary.

Thanks alot guys, I think I got it now.