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Subject: Re: [boost] Boost should not be saying "_FPOSOFF"
From: alanbirtles2 (alan.birtles_at_[hidden])
Date: 2016-09-26 16:45:38

OK, in more detail:
the actual offset in a std::streampos is "_Fpos + _Myoff".
std::streampos::seekpos returns "_Fpos"
std::streamoff(std::streampos) returns "_Myoff + _FPOSOFF(_Fpos)"
to get to the desired "_Fpos + _Myoff" we run:
std::streampos::seekpos() + std::streamoff(std::streampos) - _FPOSOFF(
std::streampos::seekpos() )
which is equivalent to:
_Fpos + std::streamoff(std::streampos) - _FPOSOFF( _Fpos )
which is equivalent to:
_Fpos + _Myoff + _FPOSOFF(_Fpos) - _FPOSOFF( _Fpos )
the two _FPOSOFF(_Fpos) cancel out to leave the desired:
_Fpos + _Myoff

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