Getting a file descriptor or a file number) for an fstream (Was: Accessing the underlying file descriptor in fstream)

[Gabriel Dos Reis]

Theodore Papadopoulo <Theodore.Papadopoulo@sophia.inria.fr> writes:

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| 
| gdr@codesourcery.com said:
| > If your need is to have a C++ ISOstream operating over a FILE* C or a
| > int, then it should be not be hard to implement your own class
| > (derived from standard stream classes) to implement your policy.
| > Passing them back to the rest of the standard algorithms should be
| > trouble-less.  
| 
| No my problem is the opposite. I have a stream and at some point I 
| want to memory map part of the file that has been open throught the 
| stream and I do not have the file name any longer.

Well let's make this straight.  The thing on top of which IOStreams are
implemented aren't directly accessible to you.  In case a number is
returned you won't know what to do with it because the lowest-level
abstraction doesn't have universal, well-defined, useful semantics;
it's just OS-specific.  Even if you ever get that number, you don't
know higher-level abstractions will interact will that lower-level
abstraction.

-- Gaby
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