eofbit lost?

[zelli]

hi all!

i want to have a look at several sequences of information, (highly probable) stored in c-strings in lines of a recuring scheme in a *.ytc. therefore i put some relevant lines in a *.txt in order to seek my favourites via c-string features. the problem is descibed below the (reduced) code:

#include <fstream>
#include <iostream>
using namespace std;

int main(){
system( "grep XB /../land.ytc > /../land.txt");
ifstream docFile( "./land.txt");

if ( docFile.is_open())
{
while ( !docFile.eof())
{
cout << " anything";
}
}
docFile.close();
return 0;
}

executing this will produce an endless loop because the eofbit is not set in my land.txt, i guess.
or the other way round: when i have a look at land.txt with less, everything is fine, ie. it appears a resonable number of lines. but executing my above code with some additions to read the lines via ifstream::getline() and so on will produce the original file for a number of resonable lines, but after 'passing the end' of land.txt it rolls on and on.

has anybody an idea what's going on and how to solve that?
cheers
Marcel

[guestgulkan]

as wriiten above - It will be an endless loop because you are not reading anything from the file, so the file read pointer does not advance through the file - so eof will always fail.

[filipe]

I don't know exactly what is going on, but you shouldn't loop on eof() because the stream might go into a fail() or bad() state and you won't know about it. You can just use the stream itself as the condition, like this:

while(docFile)
{
    // code
}

[zelli]

hi all,

looping just using the stream or alternatively the good() member function is working out.

thanks a lot!!

[zelli]

@filipe: what would be you proposal to figure out what's going on? do i need to know more about grep?

[Galik]

@zelli

You don't read anything from the file. So you will never reach the end of the file. That's what is going wrong as guestgulkan has already pointed out.