EX.7-IMPLEMENTATION-OF-SYSTEM-CALLS-READ-WRITE-FORK-OPEN-CLOSE

Aim:

C program using open, read, write, close , create , fork() system calls.

Theory:

There are 5 basic system calls that Unix provides for file I/O.

1.Create: Used to Create a new empty file

Syntax :int creat(char *filename, mode_t mode)

filename : name of the file which you want to create

mode : indicates permissions of new file.

2.open: Used to Open the file for reading, writing or both.

Syntax: int open(char *path, int flags [ , int mode ] );

Path : path to file which you want to use

flags : How you like to use

O_RDONLY: read only, O_WRONLY: write only, O_RDWR: read and write, O_CREAT: create

file if it doesn’t exist, O_EXCL: prevent creation if it already exists

3 close: Tells the operating system you are done with a file descriptor and Close the file which pointed by fd.

Syntax: int close(int fd);fd :filedescriptor

4 read: From the file indicated by the file descriptor fd, the read() function reads cnt bytes of input into the memory area indicated by buf. A successful read() updates the access time for the file.

Syntax: int read(int fd, char *buf, int size);

fd: file descripter

buf: buffer to read data from

cnt: length of buffer

5.write: Writes cnt bytes from buf to the file or socket associated with fd. cnt should not begreater

than INT_MAX (defined in the limits.h header file). If cnt is zero, write()simply returns 0without

attempting any other action.

Syntax: int write(int fd, char *buf, int size);fd: file

descripter

buf: buffer to write data to

cnt: length of buffer

*File descriptor is integer that uniquely identifies an open file of the process.

Algorithm:

1.Star the program.

2.Open a file for O_RDWR for R/W,O_CREATE for creating a file ,O_TRUNC for truncate

a file.

3.Using getchar(), read the character and stored in the string[] array.

4.The string [] array is write into a file close it.

5.Then the first is opened for read only mode and read the characters and displayed it and

close the file.

6.Use Fork().

7.Stop the program.

Program:


#include<sys/stat.h>

#include<stdio.h>

#include<fcntl.h>

#include<sys/types.h>

int main()

{

int n,i=0;

int f1,f2;

char c,strin[100];

f1=open("data",O_RDWR|O_CREAT|O_TRUNC);

while((c=getchar())!='\n')

{

strin[i++]=c;

}

strin[i]='\0';

write(f1,strin,i);

close(f1);

f2=open("data",O_RDONLY);

read(f2,strin,0);

printf("\n%s\n",strin);

close(f2);

fork();

return 0;

}

OUTPUT:

RESULT:

Thus, open, read, write, close , create , fork() system calls implemented successfully using c program.

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