using fstream within linux

Question

I think i have a beginners question.

I try to read a file line by line.

The file is in /home/myhomedir and called text.txt . The content of the file is

The file has access right for everyone to read and write.

I wanted: open the file and read it one line after another.

So I tried:

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

using namespace std;

int main(int argc, char** argv) 
{
    try
    {
        ifstream myfile ;
        myfile.open("/home/myhomedir/text.txt", ios::in);
        if(myfile.is_open())
        {
            string line;

            while (getline(myfile, line)) {
               // do nothing, just get a line
               // *
            }
        }
    }
    catch(int ex)
    {
    }

    return 0;
}

The place marked with * is reached (used the debug feature of netbeans). however line is empty and loop seemed to be entered only once.

Like if an empty file is opened.

What am I doing wrong?

You are using the try-catch-continue antipattern (unsuccessfully btw). I hope that's just a bad example. — Deduplicator
– Deduplicator, Commented Apr 27, 2014 at 11:11
Your code works well... Are you sure that your file exists ? Is it the good path ? — AntiClimacus
– AntiClimacus, Commented Apr 27, 2014 at 11:11
Could you add cout << line << endl; to the loop to see if this has to do with the optimizer? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Apr 27, 2014 at 11:15
I recommend reading How to Debug Small Programs to get a better idea of how to debug this. — Deduplicator
– Deduplicator, Commented Apr 27, 2014 at 11:37

enedil · Accepted Answer · 2014-04-27 11:26:09Z

1

The reason is, you don't know how to use debugger. I've modified your code:

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

using namespace std;

int main(int argc, char** argv)
{
    try
    {
        ifstream myfile ;
        myfile.open("/home/enedil/text.txt", ios::in);
        if(myfile.is_open())
        {
            string line;

            while (getline(myfile, line)) {
                cout << line; // there's my modification
            }
        }
    }
    catch(int ex)
    {
    }

    return 0;
}

The output is

So everything's correct.

edited Apr 27, 2014 at 11:26

answered Apr 27, 2014 at 11:18

enedil

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1 Comment

Offler Over a year ago

then it seems to be some sort of optimization. The empty loop is only entered once will the output loop is entered multiple times. while ( myfile.good()){getline(myfile, line);} does what i want (dont ask why, the file needs to be read one time without output.)

FelixM · Accepted Answer · 2014-04-27 11:17:45Z

0

If the content of the file is literally

1 2 3 4

then it has only one line and it is to be expected that "getline" returns false the second time it's called.

answered Apr 27, 2014 at 11:17

FelixM

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