How can I get a file descriptor from a c++ i/o stream?

[Thorsten Knopel]

Dear all,

Because of some reason, I must get a file descript from a c++ I/O stream,
for example: ifstream.

Under OpenUnix I have a function ifstream::fd (rdbuf->fd) to do this.
But in Linux, there is not a such function of ifstream class.
Is there not a such function in standard C++ ?
Or is there another way to get?

Thanks for your help.
Regards,
Thorsten

[Victor Bazarov]

Re: How can I get a file descriptor from a c++ i/o stream?

Thorsten Knopel wrote:[color=blue]
> Because of some reason, I must get a file descript from a c++ I/O stream,
> for example: ifstream.
>
> Under OpenUnix I have a function ifstream::fd (rdbuf->fd) to do this.
> But in Linux, there is not a such function of ifstream class.
> Is there not a such function in standard C++ ?[/color]

No. In general a stream doesn't have to have anything like a "file
descriptor" in it. It's implementation-defined how streams maintain
their association with whatever is considered "a file".
[color=blue]
> Or is there another way to get?[/color]

There can be something specific to your library implementation. Have
you tried looking in the docs or asking in a newsgroup for your OS?

V

[Pete Becker]

Re: How can I get a file descriptor from a c++ i/o stream?

Victor Bazarov wrote:[color=blue]
> It's implementation-defined how streams maintain
> their association with whatever is considered "a file".
>[/color]

It's unspecified, not implementation defined. The implementation doesn't
have to document what it does.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)