File Handling in C

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: fopen()

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

losing File: fclose()

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

int fclose( FILE *fp );

C fprintf() and fscanf()

Writing File : fprintf() function

The fprintf() function is used to write set of characters into file. It sends formatted output to a stream.
Syntax:

int fprintf(FILE *stream, const char *format [, argument, ...])

Example:

#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. It reads a word from the file and returns EOF at the end of file.
Syntax:

int fscanf(FILE *stream, const char *format [, argument, ...])

Example:

#include <stdio.h>
main(){
FILE *fp;
char buff[255];//creating char array to store data of file
fp = fopen("file.txt", "r");
while(fscanf(fp, "%s", buff)!=EOF){
printf("%s ", buff );
}
fclose(fp);
}

Output:

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

C fputc() and fgetc()

Writing File : fputc() function

The fputc() function is used to write a single character into file. It outputs a character to a stream.
Syntax:

int fputc(int c, FILE *stream)

Example:

#include <stdio.h>
main(){
FILE *fp;
fp = fopen("file1.txt", "w");//opening file
fputc('a',fp);//writing single character into file
fclose(fp);//closing file
}

file1.txt

Reading File : fgetc() function

The fgetc() function returns a single character from the file. It gets a character from the stream. It returns EOF at the end of file.
Syntax:

int fgetc(FILE *stream)

Example:

#include<stdio.h>
#include<conio.h>
void main(){
FILE *fp;
char c;
clrscr();
fp=fopen("myfile.txt","r");
while((c=fgetc(fp))!=EOF){
printf("%c",c);
}
fclose(fp);
getch();
}

myfile.txt

this is simple text message

C fputs() and fgets()

The fputs() and fgets() in C programming are used to write and read string from stream. Let's see examples of writing and reading file using fgets() and fgets() functions.

Writing File : fputs() function

The fputs() function writes a line of characters into file. It outputs string to a stream.
Syntax:

int fputs(const char *s, FILE *stream)

Example:

#include<stdio.h>
#include<conio.h>
void main(){
FILE *fp;
clrscr();
fp=fopen("myfile2.txt","w");
fputs("hello c programming",fp);
fclose(fp);
getch();
}

myfile2.txt

hello c programming

Reading File : fgets() function

The fgets() function reads a line of characters from file. It gets string from a stream.
Syntax:

char* fgets(char *s, int n, FILE *stream)

Example:

#include<stdio.h>
#include<conio.h>
void main(){
FILE *fp;
char text[300];
clrscr();
fp=fopen("myfile2.txt","r");
printf("%s",fgets(text,200,fp));
fclose(fp);
getch();
}

Output:

hello c programming

C fseek() function

The fseek() function is used to set the file pointer to the specified offset. It is used to write data into file at desired location.
Syntax:

int fseek(FILE *stream, long int offset, int whence)

There are 3 constants used in the fseek() function for whence: SEEK_SET, SEEK_CUR and SEEK_END.
Example:

#include <stdio.h>
void main(){
FILE *fp;
fp = fopen("myfile.txt","w+");
fputs("This is javatpoint", fp);
fseek( fp, 7, SEEK_SET );
fputs("sonoo jaiswal", fp);
fclose(fp);
}

myfile.txt

This is sonoo jaiswal

C rewind() function

The rewind() function sets the file pointer at the beginning of the stream. It is useful if you have to use stream many times.
Syntax:

void rewind(FILE *stream)

Example:
File: file.txt

this is a simple text

File: rewind.c

#include<stdio.h>
#include<conio.h>
void main(){
FILE *fp;
char c;
clrscr();
fp=fopen("file.txt","r");
while((c=fgetc(fp))!=EOF){
printf("%c",c);
}
rewind(fp);//moves the file pointer at beginning of the file
while((c=fgetc(fp))!=EOF){
printf("%c",c);
}
fclose(fp);
getch();
}

Output:

this is a simple textthis is a simple text

As you can see, rewind() function moves the file pointer at beginning of the file that is why "this is simple text" is printed 2 times. If you don't call rewind() function, "this is simple text" will be printed only once.

C ftell() function

The ftell() function returns the current file position of the specified stream. We can use ftell() function to get the total size of a file after moving file pointer at the end of file. We can use SEEK_END constant to move the file pointer at the end of file.
Syntax:

long int ftell(FILE *stream)

Example:
File: ftell.c

#include <stdio.h>
#include <conio.h>
void main (){
FILE *fp;
int length;
clrscr();
fp = fopen("file.txt", "r");
fseek(fp, 0, SEEK_END);
length = ftell(fp);
fclose(fp);
printf("Size of file: %d bytes", length);
getch();
}

Output:

Size of file: 21 bytes

Garima Infotech Solution

Wednesday, 3 May 2017

File Handling

File Handling in C

Advantage of File

Functions for file handling

Opening File: fopen()

losing File: fclose()

C fprintf() and fscanf()

Writing File : fprintf() function

Reading File : fscanf() function

C File Example: Storing employee information

C fputc() and fgetc()

Writing File : fputc() function

Reading File : fgetc() function

C fputs() and fgets()

Writing File : fputs() function

Reading File : fgets() function

C fseek() function

C rewind() function

C ftell() function

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