2. A files is a collection of related data
stored
In a particular area on the disk.
3. The file two associated pointers
known as the file pointers.
Each time an input or output
pointer operation takes place, the
appropriate pointer is
automatically advanced.
4. When wee open a file in read-only mode, the
input pointer is automatically set the
beginning so to that we can read the from
the start.
File is opened in ‘append’ mode.
This moves the output pointer to the end of
the file.
5. Open for reading only
input pointer
Open in append mode
(for writing more data)
output pointer
Open for writing only Output pointer
output pointer
H E L L O W O R L D
H E L L O W O R L D
6. This is possible only if we can take control of
the movement of the file pointers ourselves.
•Seekg() Moves get pointer (input) to a specified location.
•Seekp() Moves put pointer (output) to a specified location.
•tellg() Gives the pointer position of the get pointer.
•tellp() Give the current position of the put pointer.
7. infile.seekg(10);
The bytes in a file are numbered beginning
from zero.
Consider the following statement:
Ofstream fileout;
Fileout.open(“hello”,ios::app);
Int p=fileout.tellp();
8. We have just now how move a file pointer to a
desired location using the ‘seek’ functions.
start file end
outfile.seek(m );
m bytes
file pointer
9. The parameter offset represent the
number of bytes the file pointer is to be
moved from the location specified by the
parameter reposition.
• ios::beg start of the file
• ios::cur current position of the pointer
• ios::end End of the file
10. One pair of function put() and get() are
designed for handling a single character at
a time.
Another pair of functions, write() and
read(), are designed to write and read
blocks of binary data.
11. The function put() writes a single character to
the associated stream.
Similarly the function get() reads a single
character from the associated stream.
To the file using the put() function in a
It uses the function get() to fetch function file
and condition.
forloop
End-
of-file
12. #include <iostream.h>
#include <fstream.h>
#include <string.h>
int main()
{
Char string[80];
Cout<<“enter a stringn”;
Cin>>string;
int len =strlen (string);
fsteam.open(“TEXT”,ios::in | ios:: out);
for(int 1=0; i<len; i++)
file.seekg(0);
Char ch;
While(file)
{
file.get(ch);
Cout<< ch;
}
Return 0;
}
14. The function write() and read(), unlike the
function put() and get(), handle the data in
binary form.
The an in value 2594 is stored in the binary
and character formats.
But 4 digit int will take four bytes to store it
in the character form.
15. Binary format 2 bytes
character format
h ft
4 bytes
00001010 0010010
2 5 9 4
16. The binary format is more accurate for
storing the numbers as they are stored in
the exact internal representation.
The binary input and output:
vvvvv,
infile. read ((char *) & v, sizeof (v);
outfile .write ((char *) & v, sizeof (v);
17. The first is the address of the variable v, and
the second is the length of that variable in
bytes.
The address of the variable must be type
char*
The two function are used to save an array
float number display in screen.
18. The I/O system of c is that it cannot handle
user-defined data types such as class
object.
The binary input and output functions
read() and write() are designed to do
exactly this job.
The function write() copies a class object
from memory byte by byte with no
conversion.
19. The length of the object is obtained using the
sizeof operator.
The program uses ‘for’ loop for reading and
writing object.
In case the length of the file is not known we can
determine the file-size in terms of objects with
the help of the file pointer function and use it in
the ‘for’ loop or we many use while(file) test
approach to decide the end of the file.
20. The length of the object is obtained using the
sizeof operator.
The program uses ‘for’ loop for reading and
writing object.
In case the length of the file is not known we can
determine the file-size in terms of objects with
the help of the file pointer function and use it in
the ‘for’ loop or we many use while(file) test
approach to decide the end of the file.
21. Updating is a routine in the maintenance of
any data file.
o Displaying the contents of a file.
o Modifying an existing item.
o Adding a new item.
o Deleting an existing
22. In such cases, the size of each object can be
obtained using the statement:
int object_length= sizeof(object);
The, the location of a desired object say
the object may be follows:
int location = m * object_length;
The location gives the bytes number of
the first of the mth object.
File pointer to each this bytes with the
help of seekg() or seekp().
23. The program uses the “STOCK DAT” file
created using program.
operation on the file:
1. Adds a new item to the file.
2. Modifies the details of an item.
3. Displays the content of the file
24. The using files for reading and writing on the
assumption that everything is fine with the files
1. A file which we are attempting to open
for reading does not exist.
2. The file name for a new file may already exist.
3. We may attempt an invalid operation such as
reading past the end-of file.
25. 4. There which we are attempting to open for
reading does not exist.
5. We may use an invalid file name.
6. We may attempt to perform an operation
when the file is not opened for that
purpose.
The c++ file stream inherits a ‘stream-state’
member from the class ios.
26. These are supplied at the time of invoking the
program.
Used to names of data files.
Examples:
c > exam data results
The first argument argc (known as argument
counter) represent the number of argument in
the command line.
The second argument argv (known as a argument
vector) is an array of char type pointers that
point to the commands line argument.
27. C > exam data result
The value of arge would be 3 and the
argv would be an array of three
pointer to strings as shown below:
argv[0]---> exam
argv[1]---> data
argv[2]---> result
28. Note that argv[0] always represent the command that invokes the
program.
The character pointer argv[1] and argv[2] can be used name in
file.
.....
.....
infile.open(argv[1]);s
.....
.....
outfile.open(argv[2]);
.....
......
The program create two files called ODD and EVEN using the
commands-line argument and a set of numbers in an array are
written these files.
