Intro to file input/file output in C++

Hey guys, this is my second tutorial, so dont expect something insanely good. You have to download it and unzip the file fstream.doc. I wrote it in Microsoft Word and it is about 6 pages long (it has a bunch of examples and other stuff in it). Also, i would recommend that you turn off autoformatting so Microsoft Word doesnt start to move the example code around. Also, turn off spelling and grammar check unless you want a lot of funky red and green lines. Hope you like it!! Also, please email me at [email protected] if you found a bug in the code or if i made an error somewhere.

very nice.. this is a great follow up to your intro to pointers..

hehe... very nicely done man! supreme work :)

thank you very much i appriciate it :)

White,

Read both your tuts and I must say they are excellently written. Even though I'm just recently getting back into the whole C scene, I could follow along with ease... even with out any C++ experience. Nice work...

As I was going through the tutorial, freshening up my fstream knowledge, I came to an error in one of your programs and a warning in another... thought I'd let you know so you could fix it...:)

Your code:

Code:

---

#include <iostream>
#include <fstream>//includes ifstream class for file 
                      //input and ofstream class for file output
using namespace std;

int main ()
{
        ifstream fin; //creates ifstream object called fin
       
        fin.open("filename3.txt"); //opens "filename.txt"
        if (!fin.is_open()) //if you cannot open the file…
        {
                cerr << "Error 1--Cannot find or open file "filename3.txt";
                fin.clear(); //reset failbit
                return 0;
        }
       
        else
        {
                cout << "This is what is inside of filename3.txt: \n";
               
                char ch[80];
                while(fin.get(ch[80])) //reads characters from the file
                        cout << ch[80]; //prints characters to the screen
               
                fin.close();

                return 0;
        }
}

---

Fixed:

Code:

---

#include <iostream>
#include <fstream>//includes ifstream class for file 
                      //input and ofstream class for file output
using namespace std;

int main ()
{
        ifstream fin; //creates ifstream object called fin
       
        fin.open("filename3.txt"); //opens "filename.txt"
        if (!fin.is_open()) //if you cannot open the file…
        {
                cerr << "Error 1--Cannot find or open file 'filename3.txt'";
                fin.clear(); //reset failbit
                return 0;
        }
       
        else
        {
                cout << "This is what is inside of filename3.txt: \n";
               
                char ch[80];
                while(fin.get(ch[80])) //reads characters from the file
                        cout << ch[80]; //prints characters to the screen
               
                fin.close();

                return 0;
        }
}

---

And then in your final program (very nicely written), there isn't a big error but its a warning so I thought I drop it in here:

Your code:

Code:

---

#include <iostream>
#include <fstream>
#include <cstdlib>

using namespace std;

const char *fileA="bat1.txt";
const char *fileB="bat2.txt";
const char *fileC="bat3.txt";

int main (void)
{
  char ch, ch1, c[80]; //sorry for bad variable names
       
        ifstream fin, fin1, fin2; //creates 3 ifstream objects
        ofstream fout; //creates 1 fout object
       
        fin.open(fileA); //opens "bat1.txt" for reading
       
        //checks to see if "bat1.txt" can be open
        if (!fin.is_open())
        {
                cerr << "Couldn't open file " << fileA << " \n";
                return 0;
        }
       
        fin1.open(fileB); //opens "bat2.txt" for reading
       
        //checks to see if "bat2.txt" can be opened
        if (!fin1.is_open())
        {
                cerr << "Couldn't open file " << fileB << " \n";
                return 0;
        }
       
        if (fin.is_open() && fin1.is_open())
        {
          fout.open(fileC); //opens "bat3.txt" writing
          while (fin && fin)
          {
              while ((fin.get(ch)) && ch != '\n')
              {
                fout << ch; //writes content of "bat1.txt"
                                  //to "bat3.txt"
              }
              while ((fin1.get(ch1)) && (ch1 != '\n'))
              {
                fout << ch1; //writes content of "bat2.txt"
                                    //to "bat3.txt"
              }
              fout << endl;
          }
          fout.close(); //closes "bat3.txt" for writing
         
        cout << "Finished coping " << fileA << " and ";
        cout << fileB << " to " << fileC << endl << endl;
       
        cout << "This is what is inside of " << fileC << ":\n";
       
        fin2.open(fileC); //opens "bat3.txt" for reading
       
        while(fin2.get(c[80])) //reads characters from the file
                cout << c[80]; //prints characters to the screen
        }
       

       
        fin.close(); //closes "bat1.txt" for writing
        fin1.close(); //closes "bat2.txt" for writing
        fin2.close(); //closes "bat3.txt" for writing       

        // Missing a return statement...
}

---

Fixed:

Code:

---

#include <iostream>
#include <fstream>
#include <cstdlib>

using namespace std;

const char *fileA="bat1.txt";
const char *fileB="bat2.txt";
const char *fileC="bat3.txt";

int main (void)
{
  char ch, ch1, c[80]; //sorry for bad variable names
       
        ifstream fin, fin1, fin2; //creates 3 ifstream objects
        ofstream fout; //creates 1 fout object
       
        fin.open(fileA); //opens "bat1.txt" for reading
       
        //checks to see if "bat1.txt" can be open
        if (!fin.is_open())
        {
                cerr << "Couldn't open file " << fileA << " \n";
                return 0;
        }
       
        fin1.open(fileB); //opens "bat2.txt" for reading
       
        //checks to see if "bat2.txt" can be opened
        if (!fin1.is_open())
        {
                cerr << "Couldn't open file " << fileB << " \n";
                return 0;
        }
       
        if (fin.is_open() && fin1.is_open())
        {
          fout.open(fileC); //opens "bat3.txt" writing
          while (fin && fin)
          {
              while ((fin.get(ch)) && ch != '\n')
              {
                fout << ch; //writes content of "bat1.txt"
                                  //to "bat3.txt"
              }
              while ((fin1.get(ch1)) && (ch1 != '\n'))
              {
                fout << ch1; //writes content of "bat2.txt"
                                    //to "bat3.txt"
              }
              fout << endl;
          }
          fout.close(); //closes "bat3.txt" for writing
         
        cout << "Finished coping " << fileA << " and ";
        cout << fileB << " to " << fileC << endl << endl;
       
        cout << "This is what is inside of " << fileC << ":\n";
       
        fin2.open(fileC); //opens "bat3.txt" for reading
       
        while(fin2.get(c[80])) //reads characters from the file
                cout << c[80]; //prints characters to the screen
        }
       

       
        fin.close(); //closes "bat1.txt" for writing
        fin1.close(); //closes "bat2.txt" for writing
        fin2.close(); //closes "bat3.txt" for writing       

        return 0;
}

---

Anyways, very nicely written tutorial, not confusing at all and covers everything thats needed... maybe for your next tutorial you should do something like writing a header file or etc... :)

jag291

thanks for the error spotting. I actually save all of my files the comiler creates as .bat files, so i had to redo the whole code to make it .txt files. Then, i realized while i was working in Microsoft word that my comments were still using the .bat extension, so i had to change them all around. The first error you pointed out is actually an important error, and i very much appoligize. It was around 11 pm and i was making some minor corrections not in my IDE but in Mircosoft word cause i didnt want to recompile everything. Anyways, thanks again for pointing these errors out, i will defiently remember them for next time :)

besides the errors, very nice tutorial white...good work

Excellent tutorial, the only criticism I could possibly make is the use of 'using namespace std' (which I personally dislike, but a lot of people seem to use). :p

Why dont you like using namespace std;? I mean, it is a i know it is a using directive (or is it a using declaration? i always confuse those two :)) Anyways, do you think my code should have looked like this:

using std::cout;
using std::cin;
using std::endl;

or should it have looked like this:

std::cout << "Hello World" << std::endl;

its been a long time since i have done stuff like this, so i cant remember if the examples above are correct, but my final quesiton is why dont you like using "using namespace std;"?

The examples are correct, and will work in most compilers, but I just feel that writing: std::cout << (and std::endl etc.) is more technically correct.

It's no big deal at the end of the day, just a style that I follow when programming. :)

regarding the error its fine!!!!
we aRE ONLY HUMANS

BUT THE TUTORIALS IS GREAT