FILES IN C

• A file is a place on disk, where group of related data is stored.
• Two different types of data files exist in C
  1. Stream-oriented(standard) data files.
  2. System-oriented(Low-level) data files.
• Stream oriented data files are of two types
  1. Data files comprising of consecutive charecters.
  2. Unformatted data files.
• System-oriented data files are more closely related to the computers operating system.
• System oriented files are complicated to work with, their usage is comparitively limited to certain particular applications.

Basic file operations in C

1. Naming a file
2. Opening a file
3. reading data from a file
4. writing data to a file
5. closing a file.

Basics

• Before using a file, a buffer area has to be established for that file.The information is normally stored in 'buffer area' while its transfer between computer memory and datafile is being taken.
• The statement for establishing such an area is FILE *ptrvar;
• ptrvar is pointer variable name.
• FILE is a defined data type.

Opening a file

     FILE *ptrvar;
     ptrvar=fopen("filename","mode");

File opening Mode	Meaning
"r"	open an existing file read only
"w"	open a new file for write only
"a"	open an existing file appending
"r++"	open an existing file for both reading and writing
"w+"	open a new file for both reading and writing
"a++"	open an existing file for both reading and appending

Example

#include<stdio.h>

FILE *ptr;

ptr=fopen("file.txt",w);

• fopen opens the file 'file.txt' and associates it with the pointer ptr.
• "w" stands for the mode 'write-only'.

closing a datafile

• fclose(ptrvar); whrere ptrvar is pointer variable name.

Example

#include<stdio.h>

main()

{

union number

{

int one;

char two;

};

union number val;

val.one=300;

printf("val.one=%d",val.one);

printf("val.two=%d",val.two);

}

Output

value.one=300

value.two=44