From cppreference.com
pos_typepubseekoff(off_typeoff,std::ios_base::seekdirdir,std::ios_base::openmodewhich=ios_base::in|ios_base::out); (1) protected:virtualpos_typeseekoff(off_typeoff,std::ios_base::seekdirdir,std::ios_base::openmodewhich=ios_base::in|ios_base::out); (2) Sets the position indicator of the input and/or output sequence relative to some other position.
1) Calls seekoff(off,dir,which) of the most derived class.
2) The base class version of this function has no effect. The derived classes may override this function to allow relative positioning of the position indicator.
Parameters
off - relative position to set the position indicator to. dir - defines base position to apply the relative offset to. It can be one of the following constants: Constant Explanation
the beginning of a stream
the ending of a stream
the current position of stream position indicator which - defines which of the input and/or output sequences to affect. It can be one or a combination of the following constants: Constant Explanation
affect the input sequence
affect the output sequence Note
Not all combinations of parameters may be valid, see the derived versions of seekoff for details.
Return value
1) The return value of seekoff(off,dir,which)
2) The resulting absolute position as defined by the position indicator. The base class version returns pos_type(off_type(-1)).
Example
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 the base class version of seekoff returned
an undefined invalid stream position returns pos_type(off_type(-1))See also
invokes seekpos()
(public member function)
[virtual]
repositions the file position, using relative addressing
(virtual protected member function of std::basic_filebuf<CharT,Traits>)
[virtual]
repositions the next pointer in the input sequence, output sequence, or both, using relative addressing
(virtual protected member function of std::basic_stringbuf<CharT,Traits,Allocator>)
[virtual]
repositions the next pointer in the input sequence, output sequence, or both, using relative addressing
(virtual protected member function of std::strstreambuf)