Re: Testing if a file or directory exist

[Holger Kiehl <Holger.Kiehl@dwd.de>]

On Sun, 9 Sep 2007, Robert P. J. Day wrote:

> On Sun, 9 Sep 2007, Holger Kiehl wrote:
>
>> Hello
>>
>> What is the quickest way to test if a file or directory exist. I can
>> think of three different system calls that can be used: access(),
>> stat() and open(). Writting a little test program I found that this
>> is also the order of which is the quickest, that is access() is the
>> quickest and open() the slowest.
>
> if all you want to do is check for existence, then, execution time
> notwithstanding, you should use the method which accomplishes that and
> nothing more, so the obvious solution would be stat().
>
That is what I first thought as well. But I think the problem is that
stat() needs to fill up the structure with all the data, is what takes
most the time. So I thought calling stat() as follows would solve it:

      stat("abcd", NULL)

But that would fail with EFAULT (Bad address). I wonder why this is
the case, because then I assume it should be as quick as access("abcd", F_OK)
or maybe even quicker. By providing NULL as argument I tell the function
not to fillup the structure and just test if the file exist. Most proberly
POSIX defines it that way.

Holger