std::basic_streambuf<CharT,Traits>::pbump (3) - Linux Manuals
void pbump( int count );
Repositions the put pointer (pptr()) by count characters, where count may be positive or negative. No checks are done for moving the pointer outside the put area [pbase(), epptr()).
If the pointer is advanced and then overflow() is called to flush the put area to the associated character sequence, the effect is that extra count characters with undefined values are output.
count - number to add to the put pointer
Because this function takes an int, it cannot manipulate buffers larger than std::numeric_limits<int>::max() characters (LWG_255)
// Run this code
gbump (protected member function)