Re: ios::nocreate and VC++ 6.0 SP6 question

From:

"Giovanni Dicanio" <giovanni.dicanio@invalid.it>

Newsgroups:

microsoft.public.vc.mfc

Date:

Tue, 9 Oct 2007 23:52:31 +0200

Message-ID:

<ebI9G7rCIHA.4836@TK2MSFTNGP06.phx.gbl>

"Mike" <mikedavies621@yahoo.com> ha scritto nel messaggio
news:1191947138.765498.148000@d55g2000hsg.googlegroups.com...

cReadFile(std::string* fileName)
{
inputFile = new std::ifstream(fileName->c_str(), std::ios::in/* |
std::ios::nocreate*/);
ownFile = true;
};

My problem is that when I create the ifstream with a file name that
does not exist, the create succeeds and my inputFile is set to a
valid (ie non-NULL) pointer. I really need to detect when an input
file does not exist but the compiler complains that ios::nocreate does
not exist if I uncomment the remainder of the line.

Hi,

I think that ios::nocreate is non-standard (maybe this was available in some
pre-standard time-frame... but I believe it is *not* standard).

If you want to simulate ios::nocreate behaviour, you can develop code
something like this:
[Note that I don't like the use you do of pointers... I would prefer using
references instead for std::string paramter - we had a thread recently about
using references whenever possible, and pointers when you have no other
option.]

<code>
void ReadTheFile( const std::string & fileName )
{
  // Try opening the file for *read only*
  std::ifstream inputFile( fileName.c_str(), std::ios_base::in );
  if ( ! inputFile )
  {
    // File does *not* exist.
    ...
    ...

    return;
  }

  // File exists
  ...
  ...
}

</code>

Giovanni