EOF not found

Applications Programming
1

Hello,

I"m using the following c++ program on a Linux Redhat System, where it works fine.
But as soon as I move on a SunOS there will be no end of reading?

#include <fstream> 
#include <iostream>

ifstream     file("test"); 
string         buffer; 
int         i=0; 
      
 if (file.is_open()) { 
   while (!file.eof())  
   { 
     cout <<  "EOF: " << file.eof() << endl; 
          
         i++; 
        try {
         getline(file, buffer);        
          cout << i << ": "<< buffer << endl; 
         }  catch (exception& ex) { 
         cout << "ERROR READING!" <<endl;  
     }   
   } 
   file.close(); 
 }

I really don't know what to do and where it comes from?
Has anyone an idea?

Thanks Tim

2

What exactly does it do on fedora? Does it output "ERROR READING!" on fedora or not?

I can see two possible ways this program could operate depending on how its iostream works underneath. If iostream can detect EOF before a read actually fails, then it will break the while loop before any message is printed. But if it can't detect EOF until a read actually fails, then it will throw the exception and print "ERROR READING!". I'm not positive but I believe both behaviors are valid ways for iostream to work, particularly since it's hard to detect EOF on things like sockets and pipes until a read actually fails.

3

A big thank you for your reply - I'm really stuck.
So there is no error message at all:
if there a 5 lines in a textfile for example, it keeps printing out:

6: 
7:
8:
...

and so on. So the buffer is empty, but no exception is thrown, but if I put getline(file, buffer); in the while loop, like this:

while (getline(file, buffer))
  • it will return false, thus it ends when there are no more lines available.

But nevertheless I don't know why EOF fails. The same happens with file.good(). Somehow they never return false;

4

I now see that getline returns a value, which may be why it doesn't throw an exception on all systems -- it can't do both at the same time, the implementor had to pick one in the event of failure. As for why EOF doesn't occur after a failed getline, I can only guess how Sun implemented their iostream. It certainly looks like it ought to produce EOF under those circumstances. So I guess you'll just need to check all return values for errors to be compatible with both. Which is probably a good idea anyway...

so your usual while loop, and with the getline, you do this:

try{
if(getline(file, buffer) <= 0)
  break;
}

which will cause the loop to break when getline fails as well as checking for exceptions.