Re: [boost] [filesystem] dirent::d_type extension availability?

From: Neal Becker (ndbecker2_at_[hidden])
Date: 2005-12-16 21:51:56

Beman Dawes wrote:

> The directory iterator value type objects now caches status information.
> Performance is much better (6 times, in one test).
> 
> This optimization is present for the Windows API, and for POSIX systems
> which support the BSD dirent::d_type extension. Currently this is
> detected by the __USE_BSD macro. Please report other macros which
> indicate it is safe to turn on this feature.
> 
> IIRC, someone indicated that Linux also supports the feature, but
> perhaps only on later versions. If that is the case, what is the correct
>   macros to be tested for what values?
> 
> Also, Apple OS X supplies the dirent::d_type extension, but the value
> isn't actually set. Any ideas on how to activate it?
> 
> --Beman
> 
> PS: If you want to experiment, the #if test to hack is line 65 of
> .../boost/filesystem/config.hpp, current CVS head.

You'd be using readdir, then?  Well man readdir says:

       According to POSIX, the dirent structure contains a field char
d_name[]
       of  unspecified  size,  with  at most NAME_MAX characters preceding
the
       terminating null character.  Use of other fields will harm  the 
porta-
       bility  of  your  programs.  POSIX 1003.1-2001 also documents the
field
       ino_t d_ino as an XSI extension.

OTOH, the glibc header dirent.h says:
/* This file defines `struct dirent'.

   It defines the macro `_DIRENT_HAVE_D_NAMLEN' iff there is a `d_namlen'
   member that gives the length of `d_name'.

   It defines the macro `_DIRENT_HAVE_D_RECLEN' iff there is a `d_reclen'
   member that gives the size of the entire directory entry.

   It defines the macro `_DIRENT_HAVE_D_OFF' iff there is a `d_off'
   member that gives the file offset of the next directory entry.

   It defines the macro `_DIRENT_HAVE_D_TYPE' iff there is a `d_type'
   member that gives the type of the file.
 */