Explain write mode operation of files in C language

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 −

 Live Demo

#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
Enter name: ", i+1);       scanf("%s", name);       printf("Enter marks: ");       scanf("%d", &marks);       fprintf(fptr,"
Name: %s 
Marks=%d 
", 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 −

 Live Demo

#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
", eno);    printf ("employee name = %s
", ename);    printf ("salary = %f
", 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