protected virtual member function
<fstream>
streampos seekoff (streamoff off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out);
Set internal position to relative position
Sets a new position for the internal position pointers specified by parameter which. This position is calculated as an offset of off characters relative to a the origin specified by way.
Unless off is zero and way is cur, the function also writes any unwritten characters in the intermediate output buffer to the file (also calling unshift using the proper facet, when needed).
When successful, this function has the same effects as the equivalent call to fseek (see fseek for details and limitations, such as on files open in text mode).
This virtual function is called by the public member streambuf::pubseekoff.
Parameters
- off
- Offset value, relative to the way parameter.
streamoff is a signed integral type.
- way
- Object of type ios_base::seekdir, indicating the origin from which the offset is applied. It may take any of the following constant values:
| value | offset is relative to... |
|---|
| ios_base::beg | beginning of the file |
| ios_base::cur | current position of either the input position or the output position, depending on argument which.
|
| ios_base::end | end of the file |
- which
- Determines which of the internal position pointers is affected: the input position, the output position, or both. It is an object of type ios_base::openmode that, for this function, may take any combination of the following significant constant values:
| value | position pointer affected |
|---|
| ios_base::in | Modifies the input position, and its corresponding get pointer (gptr) |
| ios_base::out | Modifies the output position and its corresponding put pointer (pptr) |
Both positions may be selected simultaneously, but if both are selected when way is ios_base::cur, the function fails.
Return Value
On success, it returns the new absolute position the internal position pointer points to after the call, if representable as a value of type streampos.
On failure, or if the above is not possible, the function returns streampos(streamoff(-1)).
streampos is a positioning type that can be converted to/from integral types (an fpos type).
Data races
Modifies the filebuf object.
Concurrent access to the same file stream buffer object may introduce data races.
Exception safety
Basic guarantee: if an exception is thrown, the file stream buffer is in a valid state.
See also
- filebuf::seekpos
- Set position pointer to absolute position (protected virtual member function)
- streambuf::pubseekoff
- Set internal position pointer to relative position (public member function)