Ifstream's eof()

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January 16th, 2006, 12:38 AM

Izkata

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Ifstream's eof()

I've heard a few times that ifstream's eof() function shouldn't be used due to some innacurracy or unexpected behavoir, and that there was another way to check the file, but couldn't remember what it was. Any help?

ex:
ifstream Read;
char bar[21];
Read.open("foo.txt", ios::in);
if (!Read.eof()) Read.get(bar, 20);
Read.close();

January 16th, 2006, 01:58 AM

jafet

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Before bad() testing...

cpp Code:

Original - cpp Code
ifstream Read("filename"); // ios:in is default anyway so this is redundant if(!Read.is_open()) { cout << "Cannot open file!"; } if(Read.bad()) { cout << "Bad file!"; Read.close(); } if(Read.eof()) { cout << "Empty file!"; }

 
ifstream Read("filename"); // ios:in is default anyway so this is redundant
if(!Read.is_open())
{
    cout << "Cannot open file!";
}
if(Read.bad())
{
    cout << "Bad file!";
    Read.close();
}
if(Read.eof())
{
    cout << "Empty file!";
}

January 16th, 2006, 02:07 AM

Mazzie

Making a mistake is not sin.

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I do not know any unexpected behaviour related to eof(). But, you could also use Read.good(), which also detects other errors, not just eof. Anyways, I think you should first read from the stream, and then check if the EOF was encountered. If you first check for EOF, and then read, nothing says that the thing you read after the check is not EOF.

IE, perhaps trying:

if(Read.good()) Read.get(bar...
if(Read.eof()) //previous get returned EOF...

If you miss that check after reading from file, and then try use what you read, it may not work as expected (in case the file ended).

mm.. I hope I am clear... Although at this hour it seems quite impossible to me to be understandable :/

January 16th, 2006, 11:49 AM

Izkata

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Join Date: Feb 2004

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Bah.. It was after midnight and I didn't feel like typing the whole thing - here's a better example of what I meant:

Code:

ifstream Read;
char bar[21];
Read.open("foo.txt", ios::in);
while(!Read.eof())
{
   Read.get(bar, 20);
   Read.ignore(100, '\n');
   cout << bar << endl;
}
Read.close();

I'll remember .good(), .bad(), and .is_open(), though, and see how they work for me.. Thanks!