fstream::rdbuf() call vs. ios::rdbuf()

[Cyril Zorin]

Hello,

When I do something like this

my_fstream.ios::rdbuf(some_ptr);

to change the streambuf that the fstream uses, this actually changes
basic_ios' streambuf and does not alter fstream's streambuf.

Is this the intended behaviour? libstdc++ has a comment that due to a
design error that LWG doesn't want to correct, fstream::rdbuf() hides
both overloads of ios::rdbuf() -- but is this hiding just a "synthetic"
thing, or does fstream completely ignore basic_ios' streambuf?

Thanks,
Cyril.