@node sys/stat.h
@section @file{sys/stat.h}

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/sys_stat.h.html}

Gnulib module: sys_stat
@mindex sys_stat

Portability problems fixed by Gnulib module @code{sys_stat}:
@itemize
@item
The type @code{mode_t} is not defined on some platforms:
MSVC 14.
@item
Some macros, such as @code{S_IFMT} or @code{S_IFIFO}, are missing on some
platforms.
@item
The macros @code{S_ISBLK}, @code{S_ISCHR}, @code{S_ISDIR}, @code{S_ISFIFO},
@code{S_ISLNK}, @code{S_ISREG}, @code{S_ISSOCK} are broken on some platforms.
@item
Some platforms define macros, such as @code{S_ISDOOR}, that are not defined
on other platforms.
@item
The functions @code{lstat} and @code{mkdir} are not declared on some platforms:
mingw, MSVC 14.
@item
The macros @code{UTIME_NOW} and @code{UTIME_OMIT} are missing on some
platforms.
@item
On some platforms, @code{struct stat} does not include @code{st_atim},
@code{st_mtim}, or @code{st_ctim} members.
@mindex stat-time
Use the gnulib module
@samp{stat-time} for accessors to portably get at subsecond resolution.
@end itemize

@mindex windows-stat-inodes
Portability problems fixed by Gnulib module @code{sys_stat}, together with module @code{windows-stat-inodes}:
@itemize
@item
On Windows platforms (excluding Cygwin), @code{st_ino} is always 0.
@end itemize

On platforms where @code{off_t} is a 32-bit type, @code{struct stat}
cannot represent the size of files or block devices 2 GiB or lager
and may not work correctly on directories 2 GiB or larger.
Also, on platforms where @code{ino_t} is a 32-bit type,
@code{struct stat} cannot represent larger inode numbers.
@xref{Large File Support}, for how to address these problems.

@xref{Avoiding the year 2038 problem}, for portability issues with the
@code{time_t} components of @code{struct stat}.

Portability problems not fixed by Gnulib:
@itemize
@item
The macro @code{S_IFBLK} is missing on some platforms:
MSVC 14.
@item
On OpenVMS, @code{st_ino} is an array of three @code{ino_t} values,
not a single value.
@code{b} are known to represent the same file.
@item
On some platforms, two different files may have the same @code{st_dev}
and @code{st_ino} values, even when @code{st_ino} is nonzero:
@itemize
@item
GNU/Linux NFS servers that export all local file systems as a single
NFS file system, if a local @code{st_dev} exceeds 255, or if a local
@code{st_ino} exceeds 16777215.
@item
Network Appliance NFS servers in snapshot directories; see Network
Appliance bug #195.
@item
ClearCase MVFS; see bug id ATRia04618.
@end itemize
@item
On some file systems, @code{st_size} contains bogus information for
symlinks;
@mindex areadlink-with-size
use the Gnulib module @code{areadlink-with-size} for a
better way to get symlink contents.
@end itemize

@mindex same-inode
To partially work around porting problems with Microsoft Windows and OpenVMS,
you can use the Gnulib @code{same-inode} module to test whether two
@code{struct stat} objects are known to represent the same file.
For example, @code{psame_inode (&a, &b)} is true if the @code{struct stat}
objects @code{a} and @code{b} are known to represent the same file.

Another partial workaround is to compare other file metadata such as
@code{st_mode} and @code{st_mtime} on platforms where @code{st_dev}
and @code{st_ino} not uniquely identify a file.  However, this does
not work reliably on files whose metadata are being changed by other
programs, or where the metadata happen to be equal.
