Data Files
Many applications require the information to be written to or read from an
Many applications require the information to be written to or read from an
auxiliary memory
device.
Such information is
stored on memory device in the form of data file.
Data file allows to
store information permanently and access, alter that
information whenever
necessary
There are two
different types of data files
1. Stream oriented or
standard data files
2. System oriented or
low level data files
Stream oriented data
files are sub divided into two categories
1. Text files
consisting fo consecutive characters.
These characters can
be interpreted either by the particular library
functions used to
transfer the information or by format
specificators within
the library functions
These characters can
be interpreted as individual data items or
components or strings
or numbers
2. Unformatted data
files
It organizes data
into blocks containing continous bytes of
information.The blocks represent
more complex data structures such as an
array and structures.To process stream
oriented data files, a separate set of library functions are
used.System oriented data
files are more closely related to the computer
operating system.They are much
complicated to work upon but more efficient for certain
applications.Separate sets of
procedures with accompanying library functions are
required.Opening and closing
of a data files
The first step in a
stream oriented data files is to establish a buffer area.
The buffer area is
the temporary storage which is used while the
information is being
transfered between the computer memory and data
files.The buffer area
allows information to be read from or written to the data
files.
Establishing buffer
area
FILE *fp;
FILE is a special
structure type that establishes the buffer area.
FILE need to be
declared in upper case
fp is often referred
to as stream pointer or simply a stream.
A data file must be
opened before it can be created or processed.
This associates the
file name with the buffer area
It specifies how data
file will utilized
fp = fopen(filename,
FiletypeAttribute);
fopen is used to open
a file with the given filename, and the way the data
file will be
utilized.
The Different File
Attributes:
“r” Open an Existing
file for read only.
“w” Open a new file
for write only.
“a” Open an eisting
file for appending.
“r+” Opens a file for
reading and writing.
“w+” Open a new file
for both reading and writing.
“a+” Open an existing
file for both reading and appending.
fopen function
returns a pointer to the beginning of the buffer area
associated with the
file.
A null is returned,
if a file cannot be opened.
A data file must be
closed at the end of the program where fclose() is used
fclose(fp)
Creating a data File
:
A data file must be
created before it can be processed.
A stream oriented
data file can be created in two ways Using text editior or word processor.
Writing a program
that enters information into the computer and then writes it out to the data
file.
To Write data on to a
file :
Program
#include<stdio.h>
void main()
{
FILE *fp;
char c;
fp =
fopen("File1.dat", "w");
printf("\nEnter
Any Data from Your Key Board...\n\n");
do
{
c = getchar();
if(c >= 'a'
&& c <= 'z')
c = c - 32;
putc(c, fp);
} while(c != '\n');
fclose(fp);
}
To read data from the
file :
Program
#include<stdio.h>
void main()
{
FILE *fp;
char c;
fp =
fopen("File1.dat", "r");
if(fp == NULL)
printf("\n Error
- Can't open the file");
else
do
{
c = getc(fp);
putchar(c);
}while(c != '\n');
fclose(fp);
}
Working with Data
Blocks in Files
Structures to be
identified for all the following programs.
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
Program to accept and
write the details on to the secondary storage medium
Program
#include<stdio.h>
#include<conio.h>
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
void main()
{
char reply;
insurance p;
FILE *fp;
fp =
fopen("insurance.dat", "w");
do
{
printf("\nInsurance
Management System");
printf("\n\nEnter
The Insurance Number : ");
scanf("%d",
&p.ins_no);
printf("\nEnter
Insured Persons Name : ");
scanf("%s",
p.name);
printf("\nEnter
The Date of Insurance : ");
scanf("%d-%d-%d",
&p.doi.d, &p.doi.m, &p.doi.y);
printf("\nEnter
The Insurance Amount : ");
scanf("%f",&p.amt);
fprintf(fp, "%d
\n %s \n %d - %d - %d \n %f", p.ins_no, p.name,
p.doi.d, p.doi.m,
p.doi.y, p.amt);
printf("\nDo You
Want to Continue With Another Record [ y / n ] : ");
fflush(stdin);
reply = getchar();
} while(reply == 'y'
|| reply == 'y');
printf("\nThank
U...");
fclose(fp);
}
Program to retrive
details from the secondary storage medium and display on
the screen
Program
#include<stdio.h>
#include<conio.h>
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
void main()
{
FILE *fp;
insurance p;
clrscr();
fp =
fopen("c:\\insuranc.dat", "r");
if(fp == NULL)
{
printf("\nFatal
Error - Unable to open the File");
exit(0);
}
//fscanf(fp,
"%d\n%s\n%d-%d-%d\n %f", p.ins_no, p.name, p.doi.d, p.doi.m, p.doi.y,
p.amt);
//fprintf(fp,
"%d \n %s \n %d - %d - %d \n %f", p.ins_no, p.name, p.doi.d, p.doi.m,
p.doi.y, p.amt);
while(!feof(fp))
{
fscanf(fp,
"%d\n%s\n%d-%d-%d\n%f", p.ins_no, p.name, p.doi.d, p.doi.m, p.doi.y,
p.amt);
printf("\nThe
Insurance Number : %d", p.ins_no);
printf("\nThe
Insured Name : %s", p.name);
printf("\nThe
Date of Insurance : %d-%d-%d", p.doi.d, p.doi.m, p.doi.y);
printf("\nThe
Insured Amount : %f", p.amt);
}
printf("\nFinished
Reading");
fclose(fp);
}
Functions for
Navigations in Files
rewind (fp)
Moves the
file-pointer to the first byte in the file
fread(&NameofStructure,
RecordSize, No of Records to Read, FilePointer)
Used to Read the Data
from the File.
fwrite(&NameofStructure,
RecordSize, No of Records to Write, FilePointer)
Used to Write the
Data to the File.
fseek(&FilePointer,
Offset, Position)
Used to Move the File
Pointer to a Desired Location either forward OR
backward.
Offset:
It is the number of
bytes we want to move from the current position in
the file.
Offset is indicated
by the file pointer and can be –ve or +ve
Position:
Indicates the
location in the file from where one wishes to move.
it can be any of the
following values.
0 : Movement from
beginning of the file
1 : Movement from the
current position in the file
2 : Movement from the
end of the file
ftell()
Returns the current
file position in the file.
It returns a long
value.
Syntax:
LongVariable =
ftell(FilePointer);
long int Position;
Position = ftell(fp);
To Add and Append the
data
Program
#include<stdio.h>
#include<conio.h>
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
void main()
{
char reply;
insurance p;
insurance
accept_data();
FILE *fp;
clrscr();
printf("\nAdding
Records...Please Wait...");
fp =
fopen("C:\\insurance.dat", "ab");
if(fp == NULL)
{
printf("\nSorry!
Error in Appending the Data...");
exit(1);
}
do
{
p = accept_data();
fwrite(&p,
sizeof(p), 1, fp);
printf("\n\nAdd
Another Record? [Y/N] : ");
fflush(stdin);
reply = getchar();
}
while(reply == 'Y' ||
reply == 'y');
fclose(fp);
}
insurance
accept_data()
{
insurance x;
printf("\nEnter
Insurance Number : ");
scanf("%d",
&x.ins_no);
printf("\nEnter
The Name of The Person : ");
scanf("%s",
x.name);
printf("\nEnter
Date of Insurance (DD-MM-YYYY) : ");
scanf("%d-%d-%d",
&x.doi.d, &x.doi.m, &x.doi.y);
printf("\nEnter
The Amount Insured : ");
scanf("%f",&x.amt);
return(x);
}
To list the records
Program
#include<stdio.h>
#include<conio.h>
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
void main()
{
insurance p;
FILE *fp;
void
display_data(insurance p);
fp =
fopen("C:\\insuranc.dat", "rb");
printf("\nListing
The Records...Please Wait...");
while(fread(&p,
sizeof(p), 1, fp) == 1)
{
display_data(p);
}
fclose(fp);
}
void
display_data(insurance p)
{
printf("\nInsurance
Number : %d",p.ins_no);
printf("\nInsured
Name : %s", p.name);
printf("\nDate
of Insurance : %d-%d-%d ",p.doi.d,p.doi.m,p.doi.y);
printf("\nAmout
Insured : %f",p.amt);
}
To Modify a record
data
Program
#include<stdio.h>
#include<conio.h>
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
void main()
{
int record_no = 0;
char reply;
insurance p;
insurance
accept_data();
char name[20];
FILE *fp;
clrscr();
printf("\nProcess
for Modifying the Records.");
fp=fopen("C:\\Insuranc.dat","rb+");
if(fp == NULL)
{
printf("\nSorry!
Error in Opening The File...");
exit(1);
}
do
{
printf("\nEnter
The Name of The Person to be Modified : ");
scanf("%s",name);
record_no = 0;
while(fread(&p,
sizeof(p), 1, fp) == 1)
{
record_no++;
if(strcmp(p.name,
name) == 0)
{
printf("\nRecord
Found\t Record Number : %d ", record_no);
printf("\nEnter
The Modified Data...\n");
p = accept_data();
record_no--;
fseek(fp, record_no *
sizeof(fp), 0);
fwrite(&p,
sizeof(p), 1, fp);
break;
}
}
rewind(fp);
printf("\nDo You
Want to Modify Another Record [y/n]? : ");
fflush(stdin);
reply = getchar();
}
while(reply =='y' ||
reply == 'y');
fclose(fp);
}
insurance
accept_data()
{
insurance x;
printf("\nEnter
Insurance Number : ");
scanf("%d",
&x.ins_no);
printf("\nEnter
The Name of The Person : ");
scanf("%s",
x.name);
printf("\nEnter
Date of Insurance (DD-MM-YYYY) : ");
scanf("%d-%d-%d",
&x.doi.d, &x.doi.m, &x.doi.y);
printf("\nEnter
The Amount Insured : ");
scanf("%f",&x.amt);
return(x);
}
To Delete a record in
data
Program
#include<stdio.h>
#include<conio.h>
typedef struct
{
int d; /* Day */
int m; /* Month */
int y; /* Year */
} date;
typedef struct
{
int ins_no;
char name[20];
date doi;
float amt;
} insurance;
void main()
{
void
display_data(insurance);
insurance p;
char name[20], reply;
FILE *fp1, *fp2;
printf("\nProcess
for Deleting a Record.");
do
{
fp1 = fopen("C:\\insuranc.dat",
"rb");
fp2 =
fopen("C:\\temp.dat", "wb");
if(fp1 == NULL || fp2
== NULL)
{
printf("\nSorry!
Error in Opening The File.");
exit(1);
}
printf("\n\nEnter
The Name of The Person To Be Deleted : ");
scanf("%s",
name);
while(fread(&p, sizeof(p),
1, fp1) == 1)
{
if(strcmp(p.name,
name) == 0)
{
printf("\nRecord
Found. Displaying Data.\t");
display_data(p);
printf("\nDeleting
the Record...Are You Sure [y/n]? : ");
fflush(stdin);
reply = getchar();
break;
}
}
if(reply == 'Y' ||
reply == 'y')
{
rewind(fp1);
while(fread(&p ,
sizeof(p), 1, fp1) == 1)
{
if(strcmp(p.name,
name) != 0)
fwrite(&p,
sizeof(p), 1, fp2);
}
}
fclose(fp1);
fclose(fp2);
remove("C:\\insuranc.dat");
rename("C:\\temp.Dat",
"C:\\insuranc.dat");
printf("\nDelete
Another Record [y/n] : "); fflush(stdin);
reply = getchar();
} while(reply == 'Y'
|| reply == 'y');
}
void
display_data(insurance p)
{
printf("\nInsurance
Number : %d",p.ins_no);
printf("\nInsured
Name : %s", p.name);
printf("\nDate
of Insurance : %d-%d-%d ", p.doi.d, p.doi.m, p.doi.y);
printf("\nAmout
Insured : %f",p.amt);
}
