how do you use eof?

[anthonyv]

Hi guys I'm trying to write a program for class and I'm having trouble getting it to read all the values in the input file and outputting them. Sorry about asking this, but the teacher I have is no good and the book only does so much. Also i was wondering if i could use eof too see when it reaches the end of file, but my program says: std::string' has no member named 'eof' when i try it.

Here's my code so far. Tried using the eof in line 27:

/*#include <fstream>
#include <iostream>
#include <string>
using namespace std;

int main()
{
    string a = "fileContainingEmails.txt";
    string b = "copyPasteMyEmails.txt";
    
    //open input file
    ifstream fin;
    string fileName;
    cout<<"Enter input filename [default: fileContainingEmails.txt]: ";
    getline(cin,fileName);
    if((cin,fileName) != "")
    {
                     fileName = fileName;
    }
    else
        fileName = a;
    fin.open(fileName.c_str());
    if (!fin.good()) throw, "I/O error";
    
    while (true) 
  { 
    if(!fileName.eof());
    string lineFromFile; 
    getline(fin, lineFromFile); 
    cout << lineFromFile << endl; 
  
  fin.close();
    
    //open output file
    ofstream fout;
    string fileName1;
    cout<<"Enter input filename [default: copyPasteMyEmails.txt]"<<endl;
    cout<<"[default if value given for input: same file as input]: ";
    getline(cin, fileName1);
    if((cin,fileName1) != "")
    {
                       fileName1 = fileName1;
    }
    else if ((cin,fileName1) == "" && fileName == a)
        fileName1 = b;
    else if ((cin,fileName1) == "" &&  fileName != a)
         fileName1 = fileName;
    fout.open(fileName.c_str());
    if (!fin.good()) throw, "I/O error";
    
    cout<<endl;
    cout<<fileName<<" will be used for input."<<endl;
    cout<<fileName1<<" will be used for output."<<endl;
}
    
    
     
         return 0;
}
          
    
    
    
                 
    
*/

[Zhuge]

That if statement is completely useless; it says, if we aren't at the end of file, do nothing, then continue as normal.

[Soko]

Few things:

First, on line 25, on your while loop, you have no closing bracket, unless you copy pasted wrong.
Second, instead of a while loop (a pretest loop) you could change to a posttest loop in do/while, and use while(fin.good()).

But to answer your question, the fin.eof() should return false until eof is reached, at which time it will return true.

Why you are getting that error, I think it is because you are trying to use it on a file instead of a stream, I believe it is intended to be used on the stream. Try changing it from fileName.eof to fin.eof()

[Zhuge]

Strings don't have and eof. Files do. You probably wanted to do some_fstream.eof() instead. In any case, that if statement is useless as it does nothing.

EDIT: Beaten by there. Soko is right, there are several other errors besides that you ought to fix.

[anthonyv]

Thanks for pointing out those errors guys. I'm really new so sometimes i just throw stuff together and pray it works.

[Soko]

I have been working with c++ for half a year now (still pretty new myself) and with some projects I still do that. I throw it together, and once I have the raw raw draft of it, I fix all my errors then go from there. :)

[gcampton]

I know this is solved but the better use for it is like this:

// function process file
void procFile()
{
    string line;
    ifstream inFile("filename.txt");
    if (! inFile.is_open())
    {
        cerr << "Unable to open inFile" << endl;
        exit (1);
    }
    
    while ( ! inFile.eof())
    {
        getline(inFile, line);
        cout << line << endl;
    }
}

edit: changed is_open()

[Zhuge]

Only problem is if there was an error of some kind you would have a infinite loop. Better to loop on good().

[gcampton]

no eof marker? what kind of error?