TITLE: catching errors with ifstream

(Source: comp.lang.c++, 13 Sep 2000)

JANSEN: rutgerjansen@my-deja.com

> I'm reading data with an ifstream on the following way
>
> ifstream infile("file.txt", ios::in);
> int i;
> while(1){
> infile >> i;
> }
>
> This goes ok until there is a non-integer value in the file. How do I
> catch this?

KUEHL: Dietmar Kuehl <dietmar_kuehl@yahoo.com>

If you want to "catch" this, you would use something like this:

  infile.exceptions(std::ios_base::failbit);
  try
    {
      while (1)
        infile >> i;
    }
  catch (...)
    {
      std::cout << "error caught!\n";
    }

Of course, you would also catch an error if the file happens not to be
infinite because attempting to read something from a stream after
hitting end of file also causes a failure. Probably you just want to
use code like this:

  while (infile >> i)
    ;
  if (!infile.eof())
    std::cerr << "illegal data in the file\n";



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