Explain the write mode operation of files in C language

A file is a collection of records, or a location on your hard drive that is used to permanently store data.

Requirements for files

• When the program terminates, the entire data will be lost.

• Store data in a file and the data will be retained even if the program terminates.

• If you want to enter a large amount of data, it usually takes a lot of time to enter.

• We can easily access the contents of the file using several commands.

• You can easily move data from one computer to another without making changes.

• By using C commands, we can access files in different ways.

File operations

File operations in C programming language are as follows:

• Name the file
• Open the file
• Read from file
• Write to file
• Close file

Syntax

Statement The syntax of file pointer is as follows:

FILE *File pointer;

For example, FILE * fptr;

The syntax of naming and opening file pointer is as follows -

File pointer = fopen ("File name", "mode");

For example,

FILE *fp;
fp = fopen ("sample.txt", "w");

program1

The following is a C program for reading the names and grades of n students and storing them in a file−

Real-time demonstration

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

Program 2

The following is used to store the employee details in a file C program that creates and prints this file -

Live Demonstration

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

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