files c programming handling in computer programming

Why files are needed?
• When a program is terminated, the entire data is lost. Storing in a file
will preserve your data even if the program terminates.
• If you have to enter a large number of data, it will take a lot of time to
enter them all.
• However, if you have a file containing all the data, you can easily
access the contents of the file using a few commands in C.
• You can easily move your data from one computer to another without
any changes.

Types of Files
• When dealing with files, there are two types of files you should know
about:
• Text files
• Binary files

File Operations
• In C, you can perform four major operations on files, either text or
binary:
• Creating a new file
• Opening an existing file
• Closing a file
• Reading from and writing information to a file

Working with files
• When working with files, you need to declare a pointer of type file.
This declaration is needed for communication between the file and
the program.
• FILE *fptr;

Opening a file- for creation and edit
• Opening a file is performed using the fopen() function defined in the
stdio.h header file.
• The syntax for opening a file in standard I/O is:
• ptr = fopen("file_name","mode");
• For example,
• fopen("newprogram.txt","w");

files c programming handling in computer programming

Closing a File
• The file (both text and binary) should be closed after reading/writing.
• Closing a file is performed using the fclose() function.
• fclose(fptr);
• Here, fptr is a file pointer associated with the file to be closed.

fgets() & fputs()
• fgets() gets a string from a file
• fputs() write a string to a file
Syntax:
• fputs(string,fp);
• fgets(buffer,No.of bytes,fp);

To write data to file
#include<stdio.h>
int main()
{
FILE *fp;
char str[100];
fp=fopen("C:UsersIIIT KOTTAYAMDesktopC Programscfans.txt","w");
printf("enter string to write to the file");
gets(str);
fputs(str,fp);
fclose(fp);
return 0;
}

To read from a file
#include<stdio.h>
int main()
{
FILE *fp;
char str[100],str1[100];
fp=fopen("myfile2.txt","w");
printf("enter string to write to the file");
gets(str);
fputs(str,fp);
fclose(fp);
fp=fopen("myfile2.txt","r");
fgets(str1,100,fp);
printf("Data from the file is: ");
printf("%s",str1);
return 0;
}

fgetc()
• fgetc is a function that gets one character from a file
• This function is declared in stdio.h
• Declaration:
• fgetc(FILE *pointer);

fputc()
• fputc is a function that outputs or writes a character to a file
• This function is declared in STDIO.H
• Declaration or Syntax:
• putc(char c, FILE *pointer);

Example- To read data from console and write it to file
#include<stdio.h>
void main(){
FILE*fp;
char ch;
fp=fopen("file1.txt","w");//openingfile
ch=getchar(); // reading data from console
fputc(ch,fp);//writing single character into file
printf("%c",ch); // write data on the screen
fclose(fp);//closing file
}

Example- To read data from file and display it to screen
#include<stdio.h>
void main(){
FILE*fp;
char ch;
fp=fopen("C:UsersadminDesktopfile1.txt","r");//openingfile
ch=fgetc(fp); // reading data from file
printf("%c",ch); // write data on the screen
fclose(fp);//closing file
}

Example 1: Write to a text file
#include <stdio.h>
int main()
{
int num;
FILE *fptr;
fptr = fopen("program.txt","w");

if(fptr == NULL)
{
printf("Error!");
exit(1);
}
printf("Enter num: ");
scanf("%d",&num);
fprintf(fptr,"%d",num);
fclose(fptr);
return 0;
}

Explanation
• This program takes a number from the user and stores in the file
program.txt.
• After you compile and run this program, you can see a text file
program.txt created in your computer. When you open the file, you
can see the integer you entered.

Example 2: Read from a text file
#include <stdio.h>
#include <stdlib.h>
int main()
{
int num;
FILE *fptr;
if ((fptr = fopen("program.txt","r")) == NULL){
printf("Error! opening file");

// Program exits if the file pointer returns NULL.
exit(1);
}
fscanf(fptr,"%d", &num);
printf("Value of n=%d", num);
fclose(fptr);
return 0;
}

Explanation
• This program reads the integer present in the program.txt file and
prints it onto the screen.
• If you successfully created the file from Example 1, running this
program will get you the integer you entered.
• Other functions like fgetchar(), fputc() etc. can be used in a similar
way.

files c programming handling in computer programming

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