basic_filebuf::seekpos
Tries to alter the current positions for the controlled streams.
virtual pos_type seekpos(
pos_type _Sp,
ios_base::openmode _Which = ios_base::in | ios_base::out
);
Parameters
_Sp
The position to seek for._Which
Specifies the mode for the pointer position. The default is to allow you to modify the read and write positions.
Return Value
If the file pointer fp is a null pointer, the function fails. Otherwise, it endeavors to alter the stream position by calling fsetpos(fp, &fposn), where fposn is the fpos_t object stored in pos. If that function succeeds, the function returns pos. Otherwise, it returns an invalid stream position. To determine if the stream position is invalid, compare the return value with pos_type(off_type(-1)).
Remarks
The protected virtual member function endeavors to alter the current positions for the controlled streams. For an object of class basic_filebuf<Elem, Tr>, a stream position can be represented by an object of type fpos_t, which stores an offset and any state information needed to parse a wide stream. Offset zero designates the first element of the stream. (An object of type pos_type stores at least an fpos_t object.)
For a file opened for both reading and writing, both the input and output streams are positioned in tandem. To switch between inserting and extracting, you must call either pubseekoff or pubseekpos. Calls to pubseekoff (and hence to seekoff) have various limitations for text streams, binary streams, and wide streams.
For a wide stream, if any insertions have occurred since the stream was opened, or since the last call to streampos, the function calls overflow. It also inserts any sequence needed to restore the initial conversion state, by using the file conversion facet fac to call fac.unshift as needed. Each element byte of type char thus produced is written to the associated stream designated by the file pointer fp as if by successive calls of the form fputc(byte, fp). If the call to fac.unshift or any write fails, the function does not succeed.
Requirements
Header: <fstream>
Namespace: std