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Can someone help me understand the class FileDescriptor?

Seems like it is mainly a wrapper for this:

private int fd;

But there's no obvious way to access or set that value. Am I missing something?

On 10/12/12 3:23 PM, bob smith wrote:
> Can someone help me understand the class FileDescriptor?
>
> Seems like it is mainly a wrapper for this:
>
> private int fd;
>
> But there's no obvious way to access or set that value. Am I missing something?
>
What would you do with that value? It is generally opaque, and only
useful to pass through to other methods which already take the
FileDescriptor object.

On 10/12/2012 6:23 PM, bob smith wrote:
> Can someone help me understand the class FileDescriptor?
>
> Seems like it is mainly a wrapper for this:
>
> private int fd;
>
> But there's no obvious way to access or set that value. Am I missing something?

To quote the docs:

<docs>
Instances of the file descriptor class serve as an opaque handle to the
underlying machine-specific structure representing an open file, an open
socket, or another source or sink of bytes. The main practical use for a
file descriptor is to create a FileInputStream or FileOutputStream to
contain it.
</docs>

You can get it out from a File*Stream and you can use it to
construct a new File*Stream.

But what it contains is implementation specific and hidden
from you.

Good OOP.

On various *nix and *nix-like OS'es it could be a traditional
int fd.

Arne

On Fri, 12 Oct 2012 15:23:37 -0700 (PDT), bob smith
<> wrote, quoted or indirectly quoted someone
who said :

>Can someone help me understand the class FileDescriptor?

It is not a class you would use directly. It provides a way to hold a
platform-specific handle to an open file.

At the assembler level in Windows, when you open a file, Windows gives
you an int handle to use to read/write. You don't specify the full
filename each time or read or write, just the handle.
--
Roedy Green Canadian Mind Products http://mindprod.com
The iPhone 5 is a low end Rolex.

On 10/13/2012 4:58 PM, Roedy Green wrote:
> On Fri, 12 Oct 2012 15:23:37 -0700 (PDT), bob smith
> <> wrote, quoted or indirectly quoted someone
> who said :
>> Can someone help me understand the class FileDescriptor?
>
> It is not a class you would use directly. It provides a way to hold a
> platform-specific handle to an open file.

So far so good.

> At the assembler level in Windows,

Nope. C level.

> when you open a file, Windows gives
> you an int handle to use to read/write. You don't specify the full
> filename each time or read or write, just the handle.

That is like almost all languages and all API's.

Arne