File Pointers

1. FILE HANDLING IN
C++

2. STREAMS
A Stream is a general name given to flow of
data.
Different streams are used to represent
different kinds of data flow.
Each stream is associated with a particular
class, which contains member functions and
definitions for dealing with that particular
kind of data flow.

3. The Stream Class Hierarchy
ios
istream
get()
getline()
read()
>>
ostream
put()
write()
<<
fstreambase
iostream
Ifstream
Open()
Tellg()
Seekg()
Ofstream
Open()
Tellp()
Seekp()
fstream
NOTE : UPWARD ARROWS INDICATE
THE BASE CLASS

4. DIFFERENT FILE OPERATIONS
4OPENING A FILE
4CLOSING A FILE
4READING FROM A FILE
4WRITING ON A FILE
4CHECKING FOR END OF FILE

5. File Mode Parameters
PARAMETERMEANING
4Ios::app Append to end-of file
4Ios::ate goto end of file on opening
4Ios::binary binary file
4Ios::in
4Ios::nocreateopen fails if file doesn’t exist
4Ios::noreplaceopen fails if file already exists
4Ios::out
4Ios::trunc Deletes contents if it exists

6. FILE POINTERS

7. FILE POINTERS
4Each file object has two integer values
associated with it :
–get pointer
–put pointer
4These values specify the byte number in the
file where reading or writing will take
place.

8. File pointers…..
4By default reading pointer is set at the
beginning and writing pointer is set at the
end (when you open file in ios::app mode)
4There are times when you must take control
of the file pointers yourself so that you can
read from and write to an arbitrary location
in the file.

9. Functions associated with file
pointers :
4The seekg() and tellg() functions allow you
to set and examine the get pointer.
4The seekp() and tellp() functions allow you
to set and examine the put pointer.

10. seekg() function :
4With one argument :
seekg(k) where k is absolute position from
the beginning. The start of the file is byte 0
Begin
File
End
k bytes^
File pointer
The seekg() function with one argument

11. seekg() function :
4With two arguments :
–the first argument represents an offset from a
particular location in the file.
–the second specifies the location from which the
offset is measured.
Begin End
^
Offset from Begin
The seekg() function with two argument

12. seekg() function :
4With two arguments :
Begin
End
^
Offset from Begin
The seekg() function with two argument
^
^
Offset from end
Offset from current
position