File Related System Call - System Software Lab - Program - 8

The program for File System related system calls.
The functions like open(), read(), write(), lseek(), stat() and close() are implemented in this program.

• File System Help 
• File System Call - PPT - PDF
• UNIX System Calls

Example Program
#include unistd.
#include fcntl.h
#include sys/types.h
#include sys/stat.h

static char message[] = "hello, world";
int main()
{
int fd,op;
char buffer[80];
char fn[20];
struct stat filestat;
printf("\nEnter U'r choice 1. Write  2. Read  3.lseek 4.Exit\n");
scanf("%d",&op);
do
{
printf("\nEnter the file name to process\n");
scanf("%s",&fn);
if (op == 1)
{
fd = open(fn,O_RDWR | O_CREAT | O_EXCL, S_IREAD | S_IWRITE);
if (fd != -1)
{
 printf("%s opened for read/write access\n",fn);
 write(fd,message,sizeof(message));
 printf("Message written into %s ",fn);
 close(fd);
}
else
  printf("File %s already exists",fn);
}
else
if(op == 2)
{
fd = open(fn, O_RDWR , S_IREAD | S_IWRITE);
if (fd != -1)
 {
  read(fd, buffer, sizeof(message));
  printf("\"%s\" was read from %s\n",buffer,fn);
 }
else
  printf("**** Error Reading %s ***\n",fn);
close(fd);
}
else
if(op == 3)
{
    fd = open(fn,O_RDONLY);
    if (fd < -1)
        printf("File Error");
    else
   {
    char buf[19];
    if(read(fd,buf,20) != 20)
        printf("Less content");
    else
   {
    printf("First 20 bytes : \n %s\n ",buf);
    if(lseek(fd,20,SEEK_SET) < 0)
        printf("Not enough content");
    else
   {
    if(read(fd,buf,20) != 20)
        printf("Not Enough content");
    else
        printf("Next 20 bytes :\n%s\n",buf);
   } }}
 }
if(stat(fn,&filestat) < 0)
   printf("File not found");
else
{
printf("\nSize of the File created is : %d bytes ",filestat.st_size);
printf("\nThe user_id of the File is : %d ",filestat.st_uid);
}

printf("\nEnter U'r choice 1. Write  2. Read  3.lseek 4.Exit\n");
scanf("%d",&op);
}
while(op != 4);
printf("\nEnd of Program 8 : File related System Calls\n");
exit (0);
}