praveenvenkatt/ex.7-implementation-of-system-calls-read-write-fork-open-close

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 create(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

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 :file descriptor

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