«

-------------------------------
ifstream fin ("foo.txt");
if (!fin) cout << "Warning: Unable to open file" << endl;
-------------------------------

There are several reasons for getting that warning :
* foo.txt doesn't exist
* foo.txt exists but is busy
* etc.

Can ifstream know why it is unable to open the file?

=====================================
Alex Vinokur
private.php?do=newpm&u=
http://mathforum.org/library/view/10978.html
=====================================

"Alex Vinokur" <> writes:

> -------------------------------
> ifstream fin ("foo.txt");
> if (!fin) cout << "Warning: Unable to open file" << endl;
> -------------------------------
>
> There are several reasons for getting that warning :
> * foo.txt doesn't exist
> * foo.txt exists but is busy
> * etc.
>
> Can ifstream know why it is unable to open the file?

If it knows, it's platform-dependent (as Victor already
pointed out).
If you don't care about portability, You might want to check
if your implementation sets errno upon failure - some of them do.

HTH & kind regards
frank

--
Frank Schmitt
4SC AG phone: +49 89 700763-0
e-mail: frank DOT schmitt AT 4sc DOT com

Frank Schmitt wrote:
> "Alex Vinokur" <> writes:
>
>>Can ifstream know why it is unable to open the file?
>
>
> If it knows, it's platform-dependent (as Victor already
> pointed out).
> If you don't care about portability, You might want to check
> if your implementation sets errno upon failure - some of them do.
>

Why would checking errno require not caring about portability? errno is
standard. Either the function will set it or not. It's easy to check and
use it if it has a meaningful value.

But I don't know how common it is for implementations to set errno in
this case.

-Kevin
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