File is collection of records or is a place on hard disk, where data is stored permanently.
Need of files
Entire data is lost when a program terminates.
Storing in a file preserves the data even if, the program terminates.
If you want to enter a large amount of data, normally it takes a lot of time to enter them all.
We can easily access the content of files by using few commands.
You can easily move your data from one computer to another without changes.
By using C commands, we can access the files in different ways.
Operations on files
The operations on files in C programming language are as follows −
- Naming the file
- Opening the file
- Reading from the file
- Writing into the file
- Closing the file
Syntax
The syntax for declaring a file pointer is as follows −
FILE *File pointer;
For example, FILE * fptr;
The syntax for naming and opening a file pointer is as follows −
File pointer = fopen ("File name", "mode");For example,
FILE *fp;
fp = fopen ("sample.txt", "w");program1
Following is the C program to read name and marks of n number of students and store them in a file −
#include <stdio.h>
int main(){
char name[50];
int marks, i, num;
printf("Enter number of students: ");
scanf("%d", &num);
FILE *fptr;
fptr = (fopen("std.txt", "w")); // opening file in write mode
if(fptr == NULL){
printf("Error!");
exit(1);
}
for(i = 0; i < num; ++i){
printf("For student%d\nEnter name: ", i+1);
scanf("%s", name);
printf("Enter marks: ");
scanf("%d", &marks);
fprintf(fptr,"\nName: %s \nMarks=%d \n", name, marks);
}
fclose(fptr);
return 0;
}Output
When the above program is executed, it produces the following result −
Enter number of students: 3 For student1 Enter name: lucky Enter marks: 59 For student2 Enter name: pinky Enter marks: 89 For student3 Enter name: bob Enter marks: 45
Program2
Following is the C program for storing the details of an employee in a file and to print the same −
#include<stdio.h>
int main ( ){
FILE *fp;
int eno;
char ename[30];
float sal;
fp =fopen ("emp.txt", "w"); // opening file in write mode
printf ("enter the details of eno, ename, sal:");
scanf ("%d%s%f", &eno, ename, &sal);
fprintf (fp, "%d%s%f", eno, ename, sal);
fclose (fp);
fp = fopen ("emp.txt", "r");
fscanf (fp, "%d%s%f", &eno, ename, &sal);
printf ("employee no: = %d\n", eno);
printf ("employee name = %s\n", ename);
printf ("salary = %f\n", sal);
fclose (fp);
return 0;
}Output
When the above program is executed, it produces the following result −
enter the details of eno, ename, sal:1 Pinky 34000 employee no: = 1 employee name = Pinky salary = 34000.000000