[Bug libstdc++/45628] std::fstream::tellg invalidates I/O buffer

[paolo dot carlini at oracle dot com]

------- Comment #40 from paolo dot carlini at oracle dot com  2010-09-17 18:53 -------
In general, our users know that seeking allows to switch from reading to
writing, and viceversa (when the stream has been appropriately opened of
course). This assumption remained true for years and years. Thus, for now at
least, I would rather not change it, whether the Standard is completely clear
in this area or not.

Also, I don't think the name __is_tell is appropriate, because of course this
kinf of situation in principle can occur also when tell is not involved (like
in your testcase ;)

Modulo the above comments, I think we can enable the optimization for codecvt
too, yes, let me reformat your other tweaks and more cleanly incorporate the
!(_M_mode & ios_base::out) thing. 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45628