Contents 
Introduction
to File HandlingFile handling entitles the use of many data types. Usually
static in nature, such as int, double, char, array[size] but
dynamic inclusive like linked lists and array[size][size
undefined]. Data structures like struct are also included. In
fact, struct is the most common and useful data type used in
files.
Essentially, when reading from or writing to a file, one must
first open the file. After the file has been opened, data may be
read through the file or written to it through the use of the
client program accessing the file. To avoid trouble later with
unclosed files, programming with files does not require, but
insists that the file be closed after editing has been completed.
C++ syntax for simple file handling is done with the fstream
definition.
fstream identity;
identity.open("file and destination", ios in/out);
//opens file for //reading and writing
identity >> / << either data type or strings;
//outputs to a file, or //draws data from a file, depending on
the '>>/<<' sign
identity.close(); //file is closed
In file and Out files are established with ios::in/out and are
easier file handles then other simple ones like istream and
ostream.
EXAMPLE
Merging Two Lists:
//The following will merge two lists
from files together
//Pseudo code used
Declare file à first, second, third
Datatype dataname1, dataname2, dataname3
While(file1 has not reached it's end OR file2 has not reached
it's end)
{
open first
input dataname1 from first
open second
input dataname2 from second
if(dataname1 is proper in accordance to need)
dataname3 = dataname1
else
dataname3 = dataname2
open third
input dataname3 to third
}
close first
close second
close third
//End
Direct
Access File Handling
Direct File Access, or also known as random file access employs
methods of accessing the file by knowing the exact position in
the file where a record is located. This is determined by a
formula of essentially the following:
LOCATION = RECORD # *
LENGTH OF EACH RECORD
To employ this method, each record must be placed in a section of
a set length so that when accessing the file, the exact position
can be known and accessed very quickly without traversing the
entire list. As a result, the size of the file will probably be
much larger than that of the Sequential file at the with the
benefit of increased file access speed.
An example diagram of a direct / Random file access:
As you can see, all the records in the direct, or random access
file are located in the same sized space. Even though R 1 may be
only 2 bytes in length, it still takes up the entire 10 byte
block in the file. This required for the records in the file to
be accessed
Sequential
Access File HandlingAll the files you will place or find on most removable media
such as floppy disks, hard disks, tape backups, etc. contain
files that must be accessed through sequential file access. These
kinds of files must be accessed sequentially, like a sequential
search through a linked list. Every member of the file from
beginning to end, like every node in the linked list, must be
searched until the desired item is found. An example of this
would be like searching through a document saved as a text file
for a particular string and positioning file editing position at
that spot.
Sequentially accessed files may have records within them of any
length only restricted by the size of the medium they are placed
on. This means that sequentially accessible files, though more
difficult to traverse through, are the most efficient spacewise.
An example of a sequential file:
The Sequential File, as you can see, may have many different
sized records. In this example, some records are 1 byte, one is
10 bytes, and there are others of varying sizes. This, as can be
seen can be very efficient for disk space conservation. Next you
will see how this differs with Direct File Access and how direct
files differ.
C++ Code example of making a Sequential File Access:
do{
in_file >> temp;
}while(temp != '|'); //advances to Start of Name
in_file >> temp;
while(temp != '|'){
name += temp;
in_file >> temp;
}
Try
enteringthe Com Sci Gate
for more information!