std::strstreambuf::seekoff (3) - Linux Man Pages
virtual pos_type seekoff(off_type off,
ios_base::openmode which = ios_base::in | ios_base::out);
Repositions std::basic_streambuf::gptr and/or std::basic_streambuf::pptr, if possible, to the position that corresponds to exactly off characters from beginning, end, or current position of the get and/or put area of the buffer.
* If which includes ios_base::in and this buffer is open for reading, then repositions the read pointer std::basic_streambuf::gptr inside the get area as described below
* If which includes ios_base::out and this buffer is open for writing, then repositions the write pointer std::basic_streambuf::pptr inside the put area as described below
* If which includes both ios_base::in and ios_base::out and the buffer is open for both reading and writing, and when is either ios_base::beg or ios_base::end, then repositions both read and write pointers as described below.
* Otherwise, this function fails.
If the pointer (either gptr or pptr or both) is repositioned, it is done as follows:
1) If the pointer to be repositioned is a null pointer and the new offset newoff would be non-zero, this function fails.
2) The new pointer offset newoff of type off_type is determined
a) if way == ios_base::beg, then newoff is zero
b) if way == ios_base::cur, then newoff is the current position of the pointer (gptr()-eback() or pptr()-pbase())
c) if way == ios_base::end, then newoff is the length of the entire initialized part of the buffer (if overallocation is used, the high watermark pointer minus the beginning pointer)
3) If newoff + off is negative or out of bounds of the initialized part of the buffer, the function fails
4) Otherwise, the pointer is assigned as if by gptr() = eback() + newoff + off or pptr() = pbase() + newoff + off
off - relative position to set the next pointer(s) to
way - beg the beginning of a stream
which - Constant Explanation
pos_type(newoff) on success, pos_type(off_type(-1)) on failure and if pos_type cannot represent the resulting stream position.
// Run this code
seekpos repositions the next pointer in the input sequence, output sequence, or both using absolute addressing