On Fri, 19 Jan 2007, Tobias Ulmer wrote:
> On Fri, Jan 19, 2007 at 11:07:14AM -0500, Adam wrote:
> > Darrin Chandler <[EMAIL PROTECTED]> wrote:
> >
> > > On Thu, Jan 18, 2007 at 05:17:50PM -0500, Adam wrote:
> > > > Why does fopen()ing a directory for reading succeed instead of failing
> > > > with EISDIR? This has the possibly unexpected consequence of letting
> > > > you pass yyin to yylex() as a fopen()ed directory, which then thinks it
> > > > finished successfully because fread() returns 0 immediately.
> > >
> > > Directories are files and can be open(2)ed as such for reading.
> >
> > We're not talking about the low level open() interface, we're talking
> > about the abstracted fopen() wrapper. You can't use fread() on a
> > fopen()ed directory, and when passed a FILE * you can't tell wether its
> > a directory or just an empty file. If you can't fread() from a stream
> > that is associated with a directory, then why associate the stream with
> > a directory in the first place?
> >
> > Adam
> >
> >
>
> C* doesn't know about directories and makes no assumptions about them.
> Directories in Unix happen to be implemented as a file, so that's
> perfectly legal. Reading and writing from/to the file depends on the
> OS, and the C* standard doesn't require that this must succeed/fail.
> If and how it fails is implemented by the OS and documented here:
> http://www.opengroup.org/onlinepubs/009695399/functions/fopen.html
>
> use stat(2) before you fopen anything to make sure it's not a
> dir/device/etc (race condition...).
To avoid that race, use fstat(2) after you've opened.
-Otto
