how to get the end of the file? ios::ate doesn't work well.

[start2046]

Hello all,

I've just writen the codes to get the size of a log file:

ifstream fin("/var/log/logfile",ios::ate);
int size = fin.tellg();

But it looks like that fin's position pointer was not set correctly if anyone else were editing the logfile.That is,it looks like ios::ate was reset for sanity if the fin's file:/var/log/logfile had been edited since fin was initialized.Does it true?

And what I want to get is just the size of the logfile(maybe not the very size but exact is better),is there any suggestions?

Thanks in advance.

[Bazzy]

When you open a file in a stream, it doesn't know about the external changes the file gets while open in your program.
If you want to get the size of the file in a specific moment, close and reopen the file so it can load the new data

[writetonsharma]

If some one else is editing the file you can seek to the end of the file manually after opening the file using seekg.

fin.seekg (0, ios::end);
streampos length = is.tellg();

try this, it may help.
sometimes opening the file in binary mode helps if it has some non-printable characters. use ios::binary also while opening the file.
Otherwise try locking the file first and then open it to get the exact length of file.

[start2046]

To Bazzy:
Thanks for your reply. Well, it likes *know* the external changes.Here is the test program:

test.cpp:

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
  ifstream fin("/var/log/logfile",ios::ate); // the /var/log/logfile 's size is more than 330M
  int size = fin.tellg()/1024;   // to get the size of KB
  if( size > 204800 ) cout<<"Overflow"<<endl;
  else cout<<"logfile size ok."<<endl;
  return 0;
}

When I run the program alone, the output is:

330159
Overflow

But when I run it as soon as I save the changes on vi( by command 'w') after editing it,the output varies:

91080
logfile size ok.

Though the size on the first line is not always 91080,but it's usually less than 330159. so bewildering.

[start2046]

To writetonsharma:
Thank you for your suggestions.
I've tried that seekg-then-tellg, but got the same result.

And yes, what I do is lock the file first and then get the length, it works fine.

Well, as what I said at first, is there no other methods to get the file's size on the fly? TIA.