Standard C++ file size???

[Peter Olcott]

Is there any standard C++ way to determine the size of a
file before it is read?

[James Kanze]

On Oct 11, 3:24*am, gpderetta <gpdere...@gmai l.comwrote:

On Oct 10, 3:46 pm, Gennaro Prota <gennaro/[e-mail] wrote:

James Kanze wrote:

<snip>

Considering the original question, what about this summary:

* *Q.: Is there any standard C++ way to determine the size of a file
* *without "reading" it?

* *A.: Not a strictly conforming one: the concepts of "file size" and
* *"file read" themselves, in fact, have no universal meaning; you'll
* *have to resort to an implementation-defined mechanism, if any,
* *such as stat() on POSIX platforms, GetFileSize()/GetFileSizeEx()
* *on Win32. The system documentation, or conformity to further
* *standards such as POSIX, may/should clarify what meaning of "size"
* *and/or "read" each of those mechanisms correspond to. This may not
* *apply to all of the supported file types.

Maybe this should be a FAQ (or two :-).

BTW, I do not think that anybody mentioned in this thread that in most
systems (i.e. any system that allows concurrent access to files), the
data returned by any kind of get file size API might be stale the
instant after it has been returned.

You can't really rely on it, except to treat it as some kind of hint.
Unless of course the OS gives you some way to acquire exclusive access
to that file before the get file size request.

Yes and no. C++ certainly doesn't give you any guarantees, or
any way to get any. And even at the system level, you're not
sure of gettting any. On the other hand, you often have
practical guarantees at a higher levelthat you can more or less
count on: most programs don't handle the case where the file
contents changes gracefully, and most programs don't have to.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
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