File Handling in C Program

File Handling in c language is used to open, read, write, search or close file. It is used for permanent storage.

Advantage of File

It will contain the data even after program exit. Normally we use variable or array to store data, but data is lost after program exit. Variables and arrays are non-permanent storage medium whereas file is permanent storage medium.

Functions for file handling

There are many functions in C library to open, read, write, search and close file. A list of file functions are given below:

No.	Function	Description
1	fopen()	opens new or existing file
2	fprintf()	write data into file
3	fscanf()	reads data from file
4	fputc()	writes a character into file
5	fgetc()	reads a character from file
6	fclose()	closes the file
7	fseek()	sets the file pointer to given position
8	fputw()	writes an integer to file
9	fgetw()	reads an integer from file
10	ftell()	returns current position
11	rewind()	sets the file pointer to the beginning of the file

Opening File

The fopen() function is used to open a file. The syntax of fopen() function is given below:

FILE *fopen( const char * filename, const char * mode );  

You can use one of the following modes in the fopen() function.

Mode	Description
r	opens a text file in read mode
w	opens a text file in write mode
a	opens a text file in append mode
r+	opens a text file in read and write mode
w+	opens a text file in read and write mode
a+	opens a text file in read and write mode
rb	opens a binary file in read mode
wb	opens a binary file in write mode
ab	opens a binary file in append mode
rb+	opens a binary file in read and write mode
wb+	opens a binary file in read and write mode
ab+	opens a binary file in read and write mode

Closing File

The fclose() function is used to close a file. The syntax of fclose() function is given below:

int fclose( FILE *fp );  

Writing File : fprintf() function

The fprintf() function is used to write set of characters into file.

#include <stdio.h>  
main(){  
   FILE *fp;  
   fp = fopen("file.txt", "w");//opening file  
   fprintf(fp, "Hello file by fprintf...\n");//writing data into file  
   fclose(fp);//closing file  
}  

Reading File : fscanf() function

The fscanf() function is used to read set of characters from file.

#include <stdio.h>  
main(){  
   FILE *fp;  
   char buff[255];//creating char array to store data of file  
   fp = fopen("file.txt", "r");  
   fscanf(fp, "%s", buff);//reading data of file and writing into char array  
   printf("Data is : %s\n", buff );//printing data of char array  
   fclose(fp);  
}  

Output:

Data is : Hello file by fprintf...

C File Example: Storing employee information

Let's see a file handling example to store employee information as entered by user from console. We are going to store id, name and salary of the employee.

#include <stdio.h>  
void main()  
{  
    FILE *fptr;  
    int id;  
    char name[30];  
    float salary;  
    fptr = fopen("emp.txt", "w+");/*  open for writing */  
    if (fptr == NULL)  
    {  
        printf("File does not exists \n");  
        return;  
    }  
    printf("Enter the id\n");  
    scanf("%d", &id);  
    fprintf(fptr, "Id= %d\n", id);  
    printf("Enter the name \n");  
    scanf("%s", name);  
    fprintf(fptr, "Name= %s\n", name);  
    printf("Enter the salary\n");  
    scanf("%f", &salary);  
    fprintf(fptr, "Salary= %.2f\n", salary);  
    fclose(fptr);  
}  

Output:

Enter the id 
1
Enter the name 
sonoo
Enter the salary
120000 

Now open file from current directory. For windows operating system, go to TC\bin directory, you will see emp.txt file. It will have following information.

emp.txt

Id= 1
Name= sonoo
Salary= 120000