Files in C: MCA I

Files in C

Files are used to store data’s in the secondary memory(eg:- hard disk, floppy, flash disk etc).

There are various file operations that can be done in C like Creating a file, deleting a file, renaming a file, opening a file to read/write/append data’s etc.

Syntax for declaring a file pointer in C

FILE *file_pointer;

Eg :- FILE *fp;
Where,
FILE = keyword
*fp = user defined file pointer variable.
Once the file pointer is declared next step is to create/open a file.

Creating / opening a file in C

fopen() is used to open a specified file from disk, if it exist. If it doesn’t exist a new file will be created and opened for further file operations.

Syntax for fopen() in C

fp=fopen(“file_name with extension”,”mode”);

Where,
fp= user defined file pointer variable.
filename= name of the file with file type as extension.
mode= mode in which the file is to be opened.
Eg :-
To Read – “r”, To Write - “w”, To Append – “a”
To Read & Write – “w+”, To Read and write – “ r+” 
To Read Write with append – “a+”
In w+ mode the contents in existing file is destroyed and then can perform read/write operations.
In r+ mode just read and write operations can be performed.
In a+ mode we can perform read and write operations with appending contents. So no existing data’s in a file are destroyed.
Eg :-
fp=fopen(“data.txt”,”a+”);
After a file is opened, we have to perform read or wrote operations into it.

Writing to a file in C

fprintf()

fprintf() is used to write data’s to a file from memory.

Syntax for fprintf()

fprintf(file pointer,”control string”,variables);

eg:- fprintf(fp,”%s”,name);

Reading from a file in C

fscanf() is used to read data from a file to the memory.

Syntax for fscanf()

fscanf(file pointer,”control string”,variables);

eg:- fscanf(fp,”%s”,name);

Closing a file in C

fclose() is used to close a file in C.

Syntax for fclose()

fclose(fp);

Where, fp= user-defined file pointer.

Reading and Writing to a file in C

Sample Program :
fprintf_fscanf.c

#include<stdio.h> #include<conio.h> void main() { FILE *fp; char c[60]; int no,n; fp=fopen("data2.txt","a+"); printf("Enter the Employee Name and No : "); scanf("%s %d",c,&no); fprintf(fp,"\n\n%s\n%d",c,no); rewind(fp); printf("Enter the Employee No : "); scanf("%d",&n); while(!feof (fp)) { fscanf(fp,"%s %d",c,&no); if(no==n) { printf("\n%s \n %d",c,no); } } fclose(fp); getch(); }