My application is sort of a backup program. It stores a file's contents
in a database along with its metadata (owner/mode/mtime/etc) on a server
machine. At some later time, if needed, the file is restored to its
I've realized the current implementation is throwing away any sub-second
resolution in the last-modified time. Some platforms store both seconds
and microseconds (or nanoseconds in the case of Solaris), but the
st_mtime member retrieved by stat() only has the seconds part.
So I'm looking for two things: (1) the most portable/standard way of
getting the micro/nano second part from the stat structure and (2) the
best way to set that metadata back onto the newly restored file.
For the 'get' part, it looks like there's no standard API. Looks like a
bunch of ugly ifdefs are required. Does anyone have a sample piece of
code that handles the major platforms or just shows the way?
The 'set' part raises a question about the intention of SUS. The utime()
function is in the standard but is explicitly limited to seconds (SUSv3:
"The times in the structure utimbuf are measured in seconds since the
Epoch."). The utimes() function is also in SUS and allows microsecond
resolution ("The times in the timeval structure are measured in seconds
and microseconds since the Epoch"), but this interface is marked LEGACY
with a usage note indicating "For applications portability, the utime()
function should be used instead of utimes()". I don't get it - why would
the more capable interface be retired in favor of a dumber one? Is there
a non-legacy interface that supersedes utimes() and support setting